I see that the Phillies will air, in Philadelphia, be on both 1210 WPHT and 94.1 WIP (I'm not sure if 610 WIP will stay with sport talk during the Phillies games or also air the game).
In any case, I'll certainly try 94.1 to see how the game sounds in Stereo (the Eagles games do sound better on FM), or whatever other benefits you might get from FM vs AM. I get 94.1, 1150 and 1210 quite well at my home, so I have choices. Others may not and that's what will keep WDEL in the game. My guess, both 1150 WDEL and 1210 WPHT will take a hit in audience size as certainly the younger listeners will choose FM over AM, assuming they can get a good clear signal from WIP-FM. What also may make a difference is where you are when the game is on. I remember working at one place about 12 years ago (working shift work), and oddly enough the Wilmington AM's came in great (1150, 1290, 1450), and ONLY 93.7 and 99.5 on FM came in (no Philly FM's or AM's). So in such a situation WDEL will have the edge. My guess is, WDEL will hold on to the older demos who rarely listen to FM due to music issues and aren't really familiar with FM. Those folks will stay with WDEL. Many folks, may be regular listeners to WDEL and rather than fool around with the radio will just stay put on 1150. Those who live further down in Delaware, say below the canal or in the Newark area, may continue to listen to WDEL as they might not be able to get WIP-FM clearly.
What WDEL's engineers need to do also, is to get a better signal from the games or how their mixing it, etc. Quite often I used to end up turning to 1210 because WDEL's sound was so bassy it got muddy and irritating, yet 1210's signal was clear and with no irritating Bass. I'd tune my bass to 0 and it was still muddy. THAT's the kind of thing that will drive listeners to 1210 or 94.1.