I think this case is not possible. Rach can happen for two reasons.
1) contention free: in this case network know the rach is ongoing and hence it will not perform BWP switch until rach procedure finishes.
2) contention based:in this case ue anyways not in sync with network and hence it has to proceed with the rach procedure to get the sync back. I don't think we will receive
Any BWP switch in this state (i.e. pending rach procedure).