The seal shouldn’t fail, whether gas filled or not.
You can tell when a thermopane seal has failed, you will get condensation inside the window. At that point your window isn’t operating as a thermopane anymore, and the glass needs to be replaced.
Argon gas does slightly reduce heat transmission, it’s not as thermally conductive as air. But my feeling is that it’s a secondary factor; you should try to find a window with a nice clear Low-E coating (some have a tendency to tint the window a bit more.). Low-E reflects thermal radiation- so in winter, it helps reflect your body heat back in, reducing the ‘cold sink’ felling you get by windows; and it reflects infrared out during summer, helping to reduce heat gain. Many times, by the time you get glass with Low-E, argon gas will be included, but the added cost is so minimal you shouldn’t worry about it.
In any case, Low-E will be much more cost-effective than triple glazing (and you don’t want to know what replacing broken triple glazed panes costs)
Otherwise, I’d recommend to look for the highest quality windows you can reasonably afford. It’s one place where looking for the cheapest deal will come back to bite you.
I’m not a big fan of wholly vinyl windows. Vinyl doesn’t make a good structural material, although it usually works OK for smaller windows. Vinyl or aluminum clad wood is better, or wholly aluminum.
Also, vinyl and aluminum wil be limited in colors, as well as not allowing you to paint your house in more unique ways.