I don't think this is right. If you call time, the play is over and you don't guess at where runners would have gotten too. I don't think it matters if R3 was sliding into home with the ball in the outfield. You cannot score during a dead ball and there's no rule that allows you to award home here. The best I could think you could stretch with is the jeopardy rule. But there you have to be reversing some call.

If you kill a live ball, you do not place runners unless a specific rule tells you to (for example, when an obstructed runner is put out). 95% of the time, the get the base achieved at the moment you killed it.

What would you do with the BR in the OP; who can not be out and is no longer at bat?

1st base. Always.

Of course, just teasing you about "do not place runners unless a specific rule tells you to ". I should have included :p :p ;) ;)