In survival, earning DP is very hard, and as a result, PvE often is a place for people to grind bosses for DP.
So, instead of letting DP coming in expire, let survival players earn more DP for certain things, such as:
getting 400/500HP without buffs before the WoF/before salad boss
Dealing more than 1000 damage and toping in the top 5 (1st place gets a higher award)
Participating in boss fights in general
Just existing and not being AFK for more than 5 minutes (10DP / 30 minutes, 1 Dp for every 3 mins or something)
Getting a banner (like 3 DP, 2 DP if a water candle/battle potion is nearby/used, 1 if both are active)
Getting a rare banner (Nymph banner, Tim banner, Dr. Bones Banner, etc)
I agree with the getting in tue leader board one, this would encourage people to stay for the full boss fight instead of just getting a few hits then leaving
A suggestion (and i dont know how possible this is) but if you got dp randomly from mining, like the rarer the ore the higher chance of getting a dp or something