Thursday morning I ran to Toledo from Akron.
I drove home last night, and 6 blocks from my house, the oil light came on and all my oil appeared to have drained out.
I had the car towed to the dealer.
I drive this with the 4 cylinder and the stick:
Do I blame the dealer, that did my oil change 3 weeks back?
Absolutely. Take the receipt to them and explain what happened. It could be that they didn’t tighten it, or that they stripped it when they replaced it. Expect them to deny it, but point out that they were the last one to touch it.
Yes, it is much more common for them to over tighten it to make sure that doesn’t happen. Overtightening can lead to stripping. It is their fault and they need to fix it. I hope you shut the engine off in time to prevent damage to it. If not, likely they can weasel out of repairing it.
You can put an oil plug in at different levels of tightness.
You can over tighten and strip the threads> very bad and obvious.
You can tighten it enough to hold until the nest oil change.
You can hand tighten it in preparation to reach for the wrench. It can be just tight enough to hold for the three weeks you ran before emptying.
If it’s “3” you should have been leaking oil for some time before it fell out. But on a long trip with vibration, this all could happen on the same drive. This is the most likely cause of your failure. Someone could contend that “It lasted three weeks and someone else must have loosened it.” Technically and legally, that is possible, but not very likely. An honest dealer that does your regular service should own up to this.
Happened to me, but it wasn’t 3 weeks, it was 3 blocks. I was very lucky.
These are really difficult situations. Assuming you shut the engine off when the light came on (as opposed to driving it until it quit running), what will most likely happen is they’ll put in a new plug, fill it up with oil and send you on your merry way with no apparent problems.
But the prolonged running with very low oil and the brief running with no oil certainly caused some internal engine damage-- it’s just a question of whether that damage will manifest itself during the expected lifespan of the car. But what happens if the engine starts burning tons of oil years from now and eventually dies prematurely? It’s becomes very difficult to hang something like that on a single incident with so much time between the incident and the damage, even if it was almost certainly the main contributing factor. In some ways it can almost be better if you do run the thing 'till it dies in these situations. You’ve also got the ethical consideration of whether you can sell the car without disclosing this to buyers.
With any of these situations, be absolutely sure you get as much documented in writing as you can. It might have been better if you’d had it towed to an independent mechanic, but a missing oil plug should be obvious enough that even getting something in writing from the tow truck driver might do. If the car appears to be okay, you might even be able to get the dealer to write you a brief description of what happened (might as well get it notarized since you’re at a dealership anyways). That way, if the car takes a dive sooner rather than later you might still have some recourse against them. Before you do anything else, it might be worth consulting with a lawyer about the best way to document the incident or any other steps that might be helpful.
Fun anecdote:
My ex-mother in law ran a mid 90’s Plymouth Minivan (with a 3800 V6 engine and almost 200K on the odometer) almost 15K miles since an oil change…and this van burned oil. She’s a scatterbrain, and didn’t realize it. Anyway, the oil light came on, and according to her: “It started running strange, and made a chug-a-chug-a sound, then just died!”. She had managed to completely, and I do mean completely, empty her oil pan between oil burning off and some leaking out. Then she drove it around like normal, and it wasn’t until 10 miles from home that it quit on her.
The funny part is that after she had it towed…her daughter (my ex-wife) just dumped some oil into it, no filter change, and that van started right up and drove like nothing ever happened to it. At least…for the next 10K miles that she owned it (with no oil change). Who knows what the next owner had to deal with.
Now that’s some good engineering. 
Some cars have switches that shut off the fuel pump if the oil pressure gets too low, which prevents really spectacular no-oil engine failures. But they’re far from universal-- for whatever reason they’re common on American cars but rarer on imports. Sounds like that was the case with her minivan. It’s kind of a bit of false security because it prevents the engine from becoming a boat anchor then and there, but plenty of damage can still be done before the engine actually cuts out.
Happened to me also, but at a Jiffy Lube. Three blocks to the house, then noticed oil sprayed all over the tires and paint. Took it back and told them about it and they denied being responsible! Some choice (and profanity-laden) discussion later, they made good on it and replaced the drain plug, which they had stripped.