Most listeners, most of the time, would rather have the regular host even if he's pre-recorded. Few of them are going to remember the show from the first time it aired any way.
The Tonight Show used to have guest hosts. Now neither Tonight nor Late Night do.
TV used to use summer replacement series. Now they do summer re-runs (although limited-run summer series are starting to become commonplace).
Hannity used to sub for Rush, now he's a contender (except in Philly). Dr. Laura subbed for (and slept with) a talk show host in LA. then took his job.
All sorts of people in the biz came back from vacation to find out their sub had their job.
Don't worry. Dick Morris will announce that he is not renewing his contract after he got called into the boss' office and handed the press release announcing he's not renewing his contract to explore other options and the station wishes him well.