Here is a story - and I hate to tell it, but you did nothing wrong.
This is what
wrong looks like.
Miscellaneous Band is a functioning unit with a Decent bass player. (Who we will call
Decent Bass player.)
Miscellaneous Band records album and schedules a tour - but has yet to release album.
Decent Bass player gets called up for National Guard duty (will be gone for tour)
Mammoth Drummer calls Awesome bass player friend (Who we will call
Awesome Bass Player) to "fill in" while Decent bass player is gone on National Guard tour of duty.
Decent bass player teaches Awesome bass player parts before leaving for National Guard. (Poof!)
Awesome bass player nails songs and further embellishes his awesomeness all over the music.
Miscellaneous Band does this...
Miscellaneous Band sends Awesome bass player to RERECORD all bass parts for album before release.
Miscellaneous Band releases album with new awesome tracks from Awesome bass player.
Tours with Awesome bass player.
Band fires Decent bass player while away on National Guard Tour.
Awesome bass player leaves at end of tour during a "break."
Band explodes and evaporates into thin air.
End of story.
You did nothing wrong.
(Yeah... I know what you're thinking...)
(You're not wrong.)
I hope this makes you feel a little better.