This would mean IT would probably be gone. How do you pay PG13, GH, IT and Horford?
Step 1: Sell tickets, including for lots of playoff games
Step 2: Rake in money from TV deals
Step 3: Pay those 4 the ~$110 million or less you would owe them per year after 2018, which is still under the tax line, and be happy that Bird Rights exist
Step 4: Fill the roster with rookie contracts, underpaid guys like Crowder, and ring-chasing vets and be barely above the tax line (projected around $132 million in 2018-19, the first year of IT and PG's new contracts in this situation). And I don't see why the team wouldn't be willing to pay a bit of luxury tax to keep guys like Smart, since this team would be competing for a championship. Bradley and the 2017 pick would likely be gone in a trade for George.
Step 5: Win a couple of Championships before Horford's contract expires, and convince him to resign for less, just in time for superstar Jaylen Brown getting his max contract. Then win a couple more championships and laugh at the Lakers after winning #21 and having a 5 title lead
Okay, Step 5 might just be wishful thinking from me, but the rest would work.
Edit: Also, this thread should probably be merged with this one from a few days ago:
http://forums.celticsblog.com/index.php?topic=89939.0