We now have a keys player, but, whatever the line-up, we adapt and re-arrange anything we want to play to suit the line-up. For 'Beds Are Burning', for instance, it's the singer that 'mouths' the trombone line in the middle..! (We once had a brass section from another band do the honours; it was great..!). There are many arrangements and orchestrations that, as a 'classic' two guitars, bass and drums, we could not do as the original. No-one minds; our audiences are there to hear us, not a CD of the songs we're playing. As long as the arrangement suits your line-up, I'd say that that's enough. There are complications in using backing tracks that we wouldn't want to get involved in, s'not worth it.
Just my tuppence-worth; hope this helps.