This problem appears to have several components.
1. To discover if it is ok to go on playing with the hand in it's current condition without significant risk of serious functional injury. If yes to playing, what to do for optimum healing and return to use.
2. If it is ok, how to play with the remaining three fingers until the idex finger comes back into use.
3. How to avoid re - traumatising the index finger while playing
If you can arrange it, a visit to a BAPAM practitioner would be the first choice. If not, a visit to a GP wouldn't hurt, maybe with a further referral to physio if appropriate.
Good luck with it