The Oracle: Who's responsible for a band's debts?

A – This isn’t a simple question to answer without knowing more of the facts. For example whether your band had any written agreements or arrangements in place. On the balance of probability it is likely you are responsible for your portion of the debts incurred while in the band.
Usally when a band does business it is the individual members of the band who are the contracting party. The band does not have a separate legal existence unless it does its business via a company. If there is a band agreement it may be that the band has formed a partnership.
Even in the absence of a band or partnership agreement it may be the case that an informal partnership is deemed to come into existence as a matter of law. If the band is a partnership the individual members of the band are liable for the debts of the partnership, that is unless the partnership is a “limited partnership” (most unlikely, and you would no doubt be aware if you and your fellow members had gone to the trouble of forming a limited partnership).
Ultimately, each of the individuals behind the band are most likely responsible for the debts incurred when the band was together. Possible exceptions to this would be (1) where you had a written agreement in place between the band members saying that anyone who leaves the band has no liability for past debts (most unlikely); or (2) you specifically agreed with your creditors that debts were only repayable so long as the band were together (very unlikely); or (3) you specifically agreed with your creditors that anyone who left the band would have no liability for debts (even more unlikely!).
If your band did constitute an informal partnership then when three of the four members left it is most likely that the partnership would be deemed to have been automatically dissolved. Each member of the partnership would be deemed to assume their portion of the partnership debts. While new members may have joined “the band”, I think it is likely a new partnership would be deemed to come into existence regardless of the fact that the name of the band is the same. This new partnership would have no responsibility for old debts ( obviously remaining member of the original band would still be responsible for their portion of those old debts).
The only real way out of this would be where the new joining members gave you an indemnity in relation to prior debts at the time you left and they joined the original band.
Check any written agreements in place with your legal advisor. If there are none it sounds more likely than not that you are responsible for your portion of the debts incurred during your time with the band.