My guesses for where the CW goes in each market:
Philadelphia: WPHL 17 (Nexstar owned)
Atlanta: WPCH 17 or WATL 36
San Francisco: KRON 4 (Nexstar owned)
Seattle: KONG 16 or KZJO 22
Tampa-St. Petersburg: WTTA 38 (Nexstar owned)
Detroit: WMYD 20
Sacramento: KQCA 58 or a subchannel of KTXL 40 (KTXL is owned by Nexstar)
Pittsburgh: WPNT 22
My guesses...
Philly: WPHL 17 (your right. If so, MNT is gone in Philly.)
Atlanta: WANF 46 (Gray probably wants to give CBS up. They've hinted at dropping CBS since they've been giving it up on brandings and promotions, except for network ones. If so, WUPA becomes CBS. WATL will still be the home of MNT.)
San Francisco: KRON 4 (I'll give you that one as well. MNT goes away completely in the market.)
Seattle: KIRO 7 (Ironically enough, I say KIRO because they've done a news-intensive schedule before as a UPN affiliate. They can do the same as a CW affiliate with KSTW getting back CBS. MNT stays on KZJO.)
Tampa Bay: WTTA 38 (you're right about that too! If so, MNT goes away completely.)
Detroit: WMYD 20 or WADL 38 (It depends here. If WMYD gets it, WADL stays MNT. If WADL gets it, WMYD stays Indie, and MNT is gone completely.)
Sacramento: KTXL 40.2 (The Nexstar-owned factor matters here. MNT stays on KQCA.)
Pittsburgh: WPNT 22 (I believe you're right about this one too. I don't see WPGH giving up FOX. MNT is gone from Pittsburgh completely.)