You cant use LCS WIFI without the legacy base. The wifi box is just a mobile device interface that gives the inputs to the 990 base to send to the trains.
To the OP, if you have a TMCC base then you are still in business for running trains. Maybe not full function, but TMCC remotes will run legacy in TMCC mode. Seems silly to spend a couple hundred bucks to solve a 2 month problem and then end up with surplus.