I think it's a wonderful idea to go away this weekend and spend it w/your daughters. There is just too much hype over Valentine's Day and you know what? It's just another day for businesses to sell flowers, chocolates, cards and jewelry. What more precious is to spend time w/your children. That is something that money can't buy!
As for leaving the door ajar that is something that only you can determine. How do you normally react when your h contacts you? You can treat him in a civil manner and test the waters by being just a friend, which means listening and validating. No heavy relationship questions/talks at this time. If he should contact you, keep the conversations on neutral subjects, such as your children.
Since you and your daughters don't get together too often, you could always let him know how she's doing at college, after you return home...but that's up to you. This could be a neutral subject and one that may be of interest to him.
Just remember, if you open up the lines of communication, you need to keep your topics neutral and keep those expectations at zero at all time...and no relationship talks!
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.