The positions taken for or against Brexit have the implicit assumption that the EU will for the remainders:
Send her victorious,
Happy and glorious,
Long to reign over us,
God save the EU

Whereas for Brexit:

O lord God arise,
Scatter our enemies,
And make them fall!
Confound their knavish tricks,
Confuse their politics,
On you our hopes we fix,
God save the Queen!

To my mind there is no certainty that the EU will continue in it's present form for any length of time. This could make both positions redundant in the fullness of time.
An attempt was made to reform the institution from within. It failed.