canada
Party liability
Driving the group to the bank with the common intention to carry out the bank robbery, or with the intention of aiding the three in carrying out the bank robbery, is enough to make the driver liable as a party to the offence.
Abandonment
There is a defence of abandonment, but this requires several things (R. v. Gauthier, 2013 SCC 32 at para 50):
(1) that there was an intention to abandon or withdraw from the
unlawful purpose;
(2) that there was timely communication of this abandonment or
withdrawal from the person in question to those who wished to
continue;
(3) that the communication served unequivocal notice upon those
who wished to continue; and
(4) that the accused took, in a manner proportional to his or her
participation in the commission of the planned offence, reasonable
steps in the circumstances either to neutralize or otherwise cancel
out the effects of his or her participation or to prevent the
commission of the offence.
Application
In the circumstance you've described, it is unlikely that element (4) of the defence is made out: a significant portion of the driver's participation (driving them to the robbery) is largely undoable by this point.
Once the arrow is in the air, it is no use wishing to have never let it go — “Please God, let it miss!”
Elements (2) and (3) also seem to be missing: there was also no communication or notice to those who wanted to continue with the offence.
Arrest and charge
We cannot predict how the police or prosecution will decide to arrest or charge in the circumstances.