I kind of wish they'd just merge, but you couldn't be sure unless they made an official announcement, or they stay like that after the morning mash-up tomarrow...
I know for a fact that in the mornings, 20 on 20 simulcasts Hits 1's morning mash up from 6a-12noon.
I dont listen often at night, but when I do, I've noticed that 20 on 20 simulcasts the hits 1 nightly countdown and then switches back to 20on20 programming after it ends.