It's a good question, and one I have no answers to.
Starmer - and his inner circle - seems particularly intransigent on certain policies.
Europe is one, and benefits is another.
If the benefits policy is stopped, as seems possible ( I said possible, not likely) it will have happened through massive public pressure on MPs who see the policy as indefensible.
Could that be translated to the policy on Europe? I'm doubtful. Unless the public becomes convinced that being outside the EU is bad for their pockets there will be no pressure on MPs, and MPs aren't going to stand up to the whips unless they see their seats in jepourdy.
The only hope of Britain getting back to a sensible, serious relationship with the EU is either a Green / Lib Dem coalition government, or Trump doing something really, really stupid that forces Starmer's hand (and I fear that option in many ways).