Yeah. P2ppol is PPLNS which would brutally punish you for leaving during a block (much like Bitminter).
Backup pool is likely to be rarely uses so it should be a PPS or SMPPS or ESMPPS. You could also use Prop pool but given the income you lose to intentional hoppers and the fact there are lots of good PPS based pools I wouldn't. Score based and PPLNS would be the worst if you will be using them for variable amounts of time.
The expected value of a share under PPLNS is exactly the same as the expected value of a share under *PPS (ignoring the possibility of the collapsing SMPPS pool for the moment). With PPLNS there will be more variance in what each share actually gets paid (sometimes nothing, sometimes once, sometimes several times), but on average, the payout will be the same. There's no good reason to avoid using a PPLNS pool as a failover unless you really don't like any sort of variance.