Neither Brock Lesnar or John Cena are being advertised for any upcoming Raws by WWE as of right now, including the final show before No Mercy next week or any Raws after the PPV.
Brock Lesnar is not expected to appear on Raw next week, but he did shoot a segment, which will air next week, according to Dave Meltzer. It might be another “sit-down” interview segment like WWE has done for Lesnar’s last couple of feuds.
There’s no word on John Cena though, and not being advertised doesn’t necessarily mean that he won’t be on the show. Brock Lesnar has a set number of dates per year that WWE spreads out, but Cena shouldn’t currently be limited. He has been rumored to be taking some more time off soon though. He has a leading voice acting role in the upcoming movie Bumblebee, but there hasn’t been any concrete info if that will cause him to miss time. The movie is already in production.
According to Dave Meltzer on Wrestling Observer Radio, WWE’s original plan was for Brock Lesnar to retain the title at No Mercy, but that obviously could change. It does seem likely that WWE will try to “protect” Strowman and Lesnar either way, so there might be a screwy finish.