If a cornerback and/or linebacker is assigned to cover WR4 or WR5 in a play, but the offense comes out with a formation without a WR4 or WR5, what is the next assignment that CB and/or LB takes on.

For WR 5 should be FB to RB to TE (as Formation calls for)

For WR 4 should be RB to TE (as Formation calls for).

So if there is a FB, then the guy on WR 5 will get him, while the WR 4 should get the RB.

If no FB, but 1 RB, then WR5 is RB, WR 4 is TE.

At least as far as 'real world' is concerned.

Thank you. I'm wondering if the game's algorithm is similar.

Yes, it is the same.