Next offseason is a bit less of a worry, because Harris is expiring.  If we're looking at him as a one-year thing, no big deal.
But to absorb the Harris contract, we've got to have $39.2M of cap space.  With the new numbers out today, that means we'd have to be at $96.8M tops.  Assume that Holmes is a part of the deal.  My numbers put us at $97.7M if we renounce all cap holds but include #24 and keep Edwards and use roster charges to fill to 12 players.  If you assume that Philly is going to want #24 for Harris (seems safe) that would sneak us under that $96.8M and we could do Holmes + 24 for Harris straight up, at least if Philly is OK with that.  Obviously they lose on talent, but they save about $25M this year, and since Harden is expected to opt out they would have a metric boatload of cap space.
That kind of put us up against the wall a bit.  We would be:
Fox/Mitchell
Huerter/Monk
Murray/Edwards
Harris (Vezenkov)
Sabonis
Presumably we would then try to use the room MLE to sign Vezenkov (that's up to $7.6M three years, that should do it) and be forced to patch the rest together with min contracts.  Lyles would be a goner.  We'd be basically 8 deep with Queta or a min contract guy getting the backup C minutes.  Is that an upgrade?  Since we figure we can get Sasha either way, it's effectively Barnes (or FA replacement) + Lyles + #24 for Harris.  Hurts our depth a decent amount.