Were 48 letters put into the 1922 Committee calling for a vote of no-confidence in Boris Johnson as PM, would those members who have lost the whip be allowed to vote?
They would not be allowed to vote in the initial rounds of the election, as they are not members of the parliamentary party. Their membership has been suspended, so they cannot get the benefits of being members of the parliamentary party.
They may be allowed to vote in the final round. Reading the rules of the Conservative party suggests that there are basically two ways to get kicked out of the national party: Joining another party and bringing the party into disrepute. A member who has the whip withdrawn has not brought the party into disrepute, and if they don't join another party, then remain members of the national party and of the local Conservative association. As such they would be sent a ballot paper for the final stage of the voting process.
It is worth noting that the Conservative party has generally been willing to allow the 1922 committee to interpret and develop its own rules in response to events. The rules of the Conservative party are seen as a framework for decision making rather than immutable law.