[QUOTE=SpoilerVirgin]
{snip} …proof is discovered that the bandaged man who claimed to be Patrick is in fact Patrick, the rightful heir in line before Matthew or Matthew’s son. He marries Edith, and she becomes mistress of Downton, banishing Mary to one of the cottages. It works for me. In fact, I keep wondering if that is what Fellowes has had in mind all along.
[/QUOTE]
That’s exactly what I thought about the other day! 
BB Crawley’s position as heir presumptive is shaky. He is the 3rd cousin 2x removed to the current Earl (who is either the sixth or seventh Earl, depending on which source you consult). There may well be another 3C2R, born earlier than BB Crawley, who would thus have a superior claim to the title and estate.
Although, as Matthew Crawley’s heir, he does own part of the Downton estate. That would create some interesting conflict between Mary (who, as his mother, would manage his affairs until he reached the age of majority) and whichever new heir presumptive showed up.
But, 1925 is almost upon the Crawleys of Downton, and changes to the laws of inheritance are coming.
Be that as it may, it was not made definite that Matthew died in the crash. If Fellowes is smart, he will stick Matthew in a coma. This will allow Dan Stevens to come back to the show as a regular if he wants to. Or, he could make the occasional cameo appearance, as his schedule permits. “I’m not dead yet!”
Lady Edith Crawley is Robert Crawley’s (the Earl of Grantham, “Lord Grantham”) second daughter.
Ethel Parks is the housemaid who had an affair with Maj. Bryant and gave birth to his illegitimate son, Charlie. She ended up working as a prostitute in order to support herself and her son. Isobel Crawley hired her as a housekeeper/cook.
Edna Braithwaite is a housemaid. She was hired during Series 3. She may have been the “new maid” Edith Crawley complained about.
I do not believe that Sarah O’Brien left the soap on the bathroom floor with the intention of causing Cora Crawley (the Countess of Grantham, “Lady Grantham”) such a bad fall that she would miscarry. I think O’Brien was just looking for Cora to slip and fall on her butt, thus looking like a fool. It would be something O’Brien could snicker about to herself (and possibly to Thomas Barrow) to amuse herself when Cora was being especially demanding.
I don’t remember seeing O’Brien tell Barrow about the soap. I think O’Brien probably told Barrow about the soap when Cora had the Spanish flu. The incident and its tragic outcome may have been weighing on her conscience when she thought Cora was about to die. I find it believable that O’Brien would have consulted Barrow about whether she should confess to Cora and ask for Cora’s forgiveness.
But, I don’t know this for sure. It’s just my attempt at fanwanking.
I’m not a professional writer. However, I did take freshman composition class in college. In that class, we were taught never to sacrifice character for a joke, a gag, or a plot point. Fellowes has been, especially in the third series, sacrificing characters–especially, Lord Grantham’s–for plot twists, jokes, stunts, cliffhangers, blah blah blah. I’m not sure I want to watch the fourth series if he continues to do this.