Stu would've left eventually anyway. Actually, he was gone by the time he died.
Pete was going to be fired eventually.
George was so young, not yet sure of himself. Don't know if it would have a large immediate impact (other than butterflying away some great songs).
Only if it was Paul or John would it matter. If Paul, the group would go grittier under John's sole leadership. George might rise to junior partner, but the pop proclivities of the Beatles would be stillborn.
If John, Paul asserts himself and pulls the team further into the pop field. Less rock-ish songs. George is kept at arm's length, and maybe he leaves quite early.
Either way, without John or Paul, the group never makes it out of the Liverpool-Hamburg axis (pardon the expression). They never become what the Beatles became.