Through Saturday, outstanding qualifying offers can be rescinded unilaterally by the team. After, Saturday, however, they can only be rescinded if both parties agree.
Zeller's qualifying offer is a shade under $3.7 million. However, he will continue to take up $6.5 million of cap space, as that is his cap hold based on his Bird rights. Accordingly, even if the Celtics have no intention of signing Zeller to anything but his QO, he will take up more cap space until he does so, or until he signs elsewhere. Meanwhile, once Saturday passes, they will be unable to simply clear his cap space by waiving their hands and renouncing him -- his $6.5 million hold is there until an agreement of some sort is reached.
On the other hand, maybe the team simply doesn't have any other way to spend the money that they find suitable. In this case, waiting Zeller out might make sense.
What do you think? Will Zeller still be a restricted free agent come Sunday, will he be unrestricted, or will his situation have otherwise resolved. I think he won't be one myself, either having had his QO rescinded or by signing some sort of new contract. In other words, expect some news soon!