As a fan of a music genre where most of the artists are a few years older than me, this question has become important. If you are in an 80s band and are still touring with only a fraction of the original (or classic) lineup, at what point are you no longer that band, but are essentially a tribute band to yourself?
I don't think there is a hard rule for this. Van Halen is Van Halen as long as the Van Halen brothers are still there. I might even accept that the band can survive the departure of Alex. Yet I don't feel like Quiet Riot is really Quiet Riot when the only classic member left is Frankie Banali.
Am I being arbitrary, or is that basically fair? I don't know the answer, but that's not going to stop me from proposing some rules around this.
If the band is named after a founding member that person has to remain in the band. If the band is named after siblings the band may survive the departure of one sibling, or it may not. It'll depend on the situation.
Generally speaking, 50% of the "classic" lineup for a band must still be there for the band to be the same. This is absolutely true if the band hasn't released any new music in 7 or more years. If the band is touring in support of an album less than 2 years old, they may still have a legitimate claim on the name with less classic members. Again, it'll depend on who is still there. For example, Axl Rose touring as Guns N Roses, even though he owns the legal right to the band name, doesn't mean any of the rest of us have to accept that act as Guns N Roses.
Speaking of making new music, making music is what rock bands do, It's what separates them from the Top 40 cover band plying Friday nights at the local Holiday Inn. How long do we accept bands touring on the old stuff, without ever producing anything new? This is a complicated question, because we fans tend to not buy the new stuff, and take our bathroom break at the concert when they introduce a new song. So in some ways we are partially to blame.
I don't have a good answer, and in some ways I think it depends on the band. Twisted Sister has made it clear that they aren't making any new music, but they are happy to play a some shows every year if people are willing to keep coming. (They have announced 2016 will be the final tour). For some reason that doesn't bother me, where as Styx playing the festival circuit at less than 50% classic strength does bother me. Maybe it's a simple issue of Twisted Sister stills plays like they have something to prove on stage. When I saw Styx a couple of years ago, the stage presence had a strong we are just here for the paycheck vibe. I'm seeing Styx again in July, so we'll see if my opinion changes. Maybe they had a bad night two years ago, or maybe they were always that way, even in 1980.
I don't think I cleared anything up here, and I'm not sure if I even made a coherent point. I do think there is a line that when crossed, takes a band into tribute band to itself territory. I'm just not sure if I can identify where that damn line is, or if the line is even consistent.