IMHO, the answer depends on the group's goals. If the group doesn't really have any defined goals, you can do whatever you want...at least until other band members start to complain. Even if the group goal is to get as close to the recording as possible, you usually still have some wiggle room in your interpretation. IME it's usually acceptable to vary the bass part a bit as long as you capture the feel and style of the original bass line. How much freedom you have can vary from song to song.
A three hour gig requires 30-40 songs and we avoid music stands on stage .
You don't generally learn 30-40 new songs for every gig. My goal was generally to have about 6 hours (minimum) of material memorized. Also there are common, simple head charts beyond the 6-hours of material that competent musicians are expected to know well enough to fake your way through.
An important part of the process is how you build and maintain repertoire. I typically have the original recordings to learn new cover band material. The groups I worked in usually chose songs, scratched out a lead sheet, and provided reference recordings. Band members were expected to get the songs under their fingers before rehearsal, but memorization was not required at this point.
Something I did when I ran groups is record the band's interpretation of each song. Basically at the first rehearsal we played a song in till it was good enough for a scratch recording. This scratch recording could be used as a practice aid to memorize the song. We also recorded our concerts, so that we had higher-quality reference recordings of the final interpretation of each song.
If we needed to bring in a sub, we gave them copies of the lead sheets and reference recordings. These resources could be also used continuously by regular band members to maintain proficiency. This was especially useful if we decide to recycle material we hadn't played for a while.
A bit more perspective For someone who plays mostly for fun in one group, it should be reasonable to play all of the material fairly close to the recording, assuming that is consistent with the group's goal. 30-40 songs is not a lot of material for a decent bassist. However for a full-time professional who relies on gigs as significant part of total income, playing everything strictly note for note is not reasonable. A full-time pro may play in all sorts of different musical situations and need to know hundreds, if not thousands of songs. At some point, it becomes unrealistic to play every song strictly note for note. However a player at this level should have the skills and experience to play freely while honoring the original style and feel. They should also have the skill and experience to play the song totally different.