If my husband dies before me, then he'd want me to go on and do whatever makes me happy in life, whether that'd include a new partner or not. I feel the same way. If I die first, then I'd want him to find someone new, if that was what made him happy - but both of us agree that the children come first, no matter what. I don't think human beings are meant to be solitary, but some people prefer it that way, so it's a question that can't easily be answered.
Age is no barrier to love, so it's always possible for people to meet someone else in the future, but you never forget the memories of what's been before, which is how it should be.