Well, if there were ice crystals then there is a chance you lysed some of the yeast. It's really impossible to tell how much the yield was decreased by the freeze/thaw, but is is promising that the package expanded when warmed.
My advice would be to use another package of yeast if you can get one, and just pitch both packages. It is entirely possible that you still have plenty of yeast in the package you have, but for my time and money a few extra dollars is worth it to prevent a possible slow/stressed fermentation. If you don't have access to a LHBS and you want to go ahead with your brew day as planned, that's definitely an option as well. Just pitch the yeast you have and keep your fingers crossed.