Well, we definitely won't see him in 2028, at least not under this contract. But also the season might not even start until July of 2027. It's not unheard of to come back after 11-12 months, though very much best-case.
Ultimately I would agree the Phillies can't count on Keller and Kerkering and still don't really know what they have in Killian and Bowlan, so they are going to have to sign or trade for at least two relievers (one RHP, one LHP).