Maybe I do not understand MaxPPS correctly, but ...
what happens if there is a long dry spell?

The missing solved blocks will lead to the pool being short on funds.
Short funds means less than expected PPS.
If the current PPS goes too low, people will leave.
With less people mining it will take longer for things to average out.
The longer it takes, the more people leave.

So you may potentially be setting yourself up for a dead pool if a long dry spell hits.

What am I missing?