Mmm... Maulerfiends? I bet
SS/
TH terminators do trouble you, they'll save your attacks on a 3+, no matter what, while they'll easily answer with some penetrating hits.. enough to eventually roll a 5+ and make you explode.
I understand you like them, but I believe that after Possessed and the Helbrute they are the worst choice in the codex.
AV 12 is way too easy to penetrate, you have only 4 attacks on the charge (plus one with the magma cutter, because it's unlikely that with
WS 3 you'll hit with all 4 of them). Yes, they are 4 powerfists, so they hurt a lot. But half of them are bound to miss, and 1s to hit are more common than you think. On the other hand, you just need a well placed hit to blow up
Terminators do succumb to anything that will make them throw lots of dice.
Do you want a good, cheap example of a unit that is the doom of all kind of terminators? 20 Daemonettes with an Herald of Slaanesh and the Exalted Locus of Beguilement. Trust me, if at least 10 of them and the herald reach close combat, there is no way for a terminator squad to surive that, too many rending attacks. Those 21 models just cost 255 points, a steal if you pose enough immediate threat to allow them to reach
CC relatively unharmed.
If i were you I would drop the cultists and the Maulerfiends, take some Havocs/Obliterators, one Heldrake and ally with Daemons to take an Herald of Slaanesh, 20 Daemonettes and 10 Plaguebearers to camp the objective (they cost the same, but are more reliable than cultists).
But if you say that you absolutely want to have Bile, an horde of marines and 3 Maulerfiends... you already have your list, no much room for change, so I wonder why you posted here