Nurgle Spawn are very strong at both making a good attempt at keeping up with bikes, and are very hard for the bikes to actually kill.
Well, barring plasma. But they do make a good counter to grav.
Melee infantry like zerkers are a bad idea--no way to keep up. And his bikes will have the edge of a pile of special rules over yours (though I suppose you will have marks--higher I and FNP for Slaaneshi bikers sounds tempting...).
I would say bring your other main AP3 Ignores Cover weapon you have available, if Noise Marines are out and the Heldrake is already in--a biker Lord with the BBoS. And a lightning claw, probably, though a power fist might be useful if some Deathwing make an appearance... (or just cracking pesky artificier armor on a character)
Not having a Maulerfiend or two is disappointing, since those could crash right in real fast and make a mess of enemy biker squads. Hmm, Havocs with missile launchers for some nice krak shots? Oblits would also make for a decent swiss-army knife.
The Vindis... probably aren't a good idea, given how short a range they have and how easy that would make it for bikes to, say, get into side armor melta range (though they may have to jink to survive--still, then they assault in for HoW and krak grenades against your rear AV10). Or they might just get immobilized by grav while his hyper-mobile bikers dance around its threat cone for the rest of the game. The numbers might change a bit with multiple of those Vindis in overlapping fields of fire with bubble-wrap cultists to protect them from assault, and all, but... that's a lot of points and effort to get the best out of a match-up that isn't going your way from the start. Now, if you were up against a Deathwing army... provided you survived their alpha strike (say, started the Vindis in reserve so the Termis didn't DS into their rear/side arc with cyclones), they would wreak all sorts of hell.
I might go Crimson Slaughter for a Balestar sorc--if you are ML3, you have a fair shot at rolling up Perfect Timing to give those MissileHavocs some Ignores Cover. And if not, well, Prescience is never a bad thing.
With their tough bodies and double cover/armor saves, combat with AP3 weapons feels like the place to be... just it's hard to see how to get there, without Maulerfiends and with your own bikes looking pretty basic next to the heap of special rules theirs get.