There is a return proposal (which gets votes like any other). Any proposals that get more votes than return get paid (until total funding runs out). Once the funding payout process reaches return, the remaining budget is put back in the pool and proposals below return are not funded.
The first thing I'm going to do immediately after activation is vote for return and I encourage others to do the same, then I will evaluate other proposals.
RE: HF21: SPS and EIP Explained