The romantic side of me has always wanted Sarah and Andrew to remarry, but for years, I honestly didn't think it would happen. More recently, though, I've changed my mind. There are so many little signs that point to a remarriage in the next decade or so for Andrew and Sarah. I agree that, just like Charles "waited" (we think) until after the Queen Mother died to marry Camilla, Andrew also wouldn't marry Sarah until after Prince Philip passed. After that, though, I doubt the Queen would stand in the way of a remarriage, as long as she was reasonably sure that a remarriage wouldn't create any major new scandals. She seems to be fairly easy on her children and to want them to be happy.
As for public opinion on a remarriage, I think it would be divided. Didn't Andrew get better press than Sarah at the time of their separation/divorce? And yet nowadays, I really believe the media nowadays is more vicious towards Andrew than Sarah--it repeatedly accuses him of wasting millions of taxpayer dollars and being callously indifferent to the average taxpayer. The segment of the population that criticizes Andrew now would probably be against a remarriage--more waste of money, another "useless" York to trade in on her royal connections, etc. But I think the segment of the British population that feels negatively towards Andrew will feel that way whether Andrew remarries Sarah or not.
On the other hand, I suspect (although I don't know this, I don't live in Britain and I've never done a poll!) that another segment of the population would find a remarriage between Andrew and Sarah to be romantic and would see Sarah as an asset to the royal family. If I read news articles about Andrew, the comments seem to be generally negative. On the other hand, I frequently read comments from people supporting Sarah--praising her for rebuilding her life and having the courage to speak up about various issues, and wishing aloud that she would reunite with Andrew. Sarah does have fans. Yes, she will also always have detractors, but so will the monarchy.
I think it would be tricky for Andrew and Sarah to get back together and the circumstances would have to be absolutely right, but I think that if Sarah ever feels strongly enough about remarrying Andrew, it will happen. Other than Philip, I've always thought that the only real obstacle to a remarriage between Sarah and Andrew is whether Sarah would want it. Why would she want to go back to a family she felt didn't treat her well, why would she return to a British press that wrote scathingly about her 'vulgarity' and weight? If she wants to keep the "perks" of being royal without having to follow the protocol, she would keep things as they are right now. But...this spring especially, she gave a lot of interviews to promote "The Young Victoria", and in every single interview I really noticed how much she seemed to want to go back to Britain, to "do things over again" with Andrew (even 17 years after their separation!). The really telling comment was when someone asked her if she would ever remarry Andrew and her answer amounted to "I'm not sure, I'd have to think about it, maybe I'm older and wiser now," which was really interesting because I know for certain that for years, her answer to those kind of questions has always been a flat-out "no, we're better off as friends."
I think if Sarah talks that way, then she is not content with the way her life is right now and that eventually she will fight to re-enter the royal family. Just my opinion! I don't think it will happen right away, but I definitely wouldn't count out a remarriage between Andrew and Sarah, especially not if Sarah wants it. People may not always care for her and sometimes I find her a bit "much," but whenever Sarah has wanted something in the past--to pay off her debts, to lose weight, to make a movie about Queen Victoria--she has always worked until she has achieved it.