Yup, I think Crimea is very much dependent on Western support. It's certainly quite plausible Ukraine could take it back with continued support, but with Putin still in power and throwing resources into this war then it would be very hard otherwise and there could be pressure for a peace deal at some point before then.
I guess one scenario that could make it more likely would be Ukraine getting further big wins in the south; Russian forces in Kherson and Zaporoska oblast collapsing and that prompts serious unrest in Russia or even Putin being deposed. IF Russia has a change of leadership or serious unrest or even a civil war/breakup to contend with then Ukraine can very plausibly keep pushing and drive Russians out of Crimea.
I'm in two minds about the bridge, on one hand it would be great to see and would really really upset Putin and cause Crimeans to panic, on the other hand, depending on the progress made, that might be their main escape route, you perhaps want hundreds of thousands of Russians to flee over that thing.
One half-way solution might be to blow up the rail bridge only, which achieves the goal of making resupply far more difficult (Russians relying on trains), they're then forced to stretch out their already difficult logistics via trucks.