Well, the 501, 502, and 503 streetcar lines won't be terminated when the subway is built. I personally think they should keep the lines for local services along the subway route, but they can also have them run into a streetcar subway terminal at Queen-Sherbourne station.
Eliminating either streetcar route along the entire corridor in my eyes is a terrible idea for the current DRL, there are far too few stations for it to be justified, however, if we have to end up splitting the queen or King streetcars, we can rename them 501-Neville (Terminates at Queen-Sherbourne), 502-Kingston Rd (terminates at Queen-Sherbourne), 503-Downtowner (current alignment or reroute it along Parliament to Union. 504-King (The subway station west of University on King if Built to Broadview), 507-Long Branch (wherever the end of the DRL on queen is to Long Branch), 508-Lakeshore OR Roncessvales (End of DRL West on King to Dundas West), 514-Cherry (Same terminus at the DRL as the 504).