i'm glad to hear you supported the garden spider and her egg laying efforts, it's a nice surprise to see people take a positive interest in these creatures (most people are freaked out by spiders). spring may not happen for these eggs until later in june, though it does seem they should have hatched given the warmth. i've got a few questions which may help us figure out if the eggs are dead. has it been very dry lately or over the winter? does the window sit in the sun for any period of time (reflected light may dehydrate the egg sacs making them unlikely to ever hatch)? if neither of those factors seem likely and they still don't hatch by mid june, it might be they just may never hatch. to be on the safe side, if by that time they haven't hatched, you may want to gently take the egg sac and place it in a safe area outside in the yard and hope for the best. that way you will be able to wash your windows without destroying the eggs if they're still viable but just late.
garden spider egg sacs are pretty sturdy and can withstand quite a bit so no, it probably wouldn't deflate if the spiderlings left. i doubt you would have missed them leaving the egg sac though, small as they are. we had a hopping spider egg sac hatch in our kitchen window and there were dozens of little hopping spiders everywhere, i had to take them all outside individually and by twos (quite a task) because my sister was threatening to be the death of them. you'd probably see the little guys everywhere on the outside of your window if they hatched. but, as everything in nature is never a complete given, you may have missed the hatching and they all left. well, that's about the extent of the info i can give, i wish you luck with your spiders, i do hope they end up hatching :)
