Do those followers go to the Wall though? Who knows.

That's a different situation, but yes. There have been cases where a deity kills another and masquerades as that god, continuing to grant spells to the gods followers. It's happened a number of times and each case has been pretty unique.

Two recent cases that are ongoing are the situation with Set killing Sseth recently and Auril sucking away Ulutiu's powers. With Sseth, Set captured him first, before finally killing him and taking his powers. During his capture, Sseth was able to send out cryptic messages of distress to his followers. Sseths followers interpreted this in many ways. The two main interpretations were that Sseth was angry with them or that Sseth was in trouble. At the end, some follower even learned that Sseth was dead, when he suddenly went silent after so many cryptic and chaotic messages sent.

With Ulutiu, it's different. Ulutiu has been slumbering for some time, so his silence is nothing new. Auril is slowly sucking his divinity away. Just slow enough not to wake him. Because of that, his followers are none the wiser.

Do those followers go to the Wall though? Who knows.

On the issue of whether or not followers of dead powers go to the wall, I would really think it would be a case dependent on the deity and his/her former allies.

but if thats true.... then if devils can take souls if they are willing why cant other deitys, or do faithless and the false not get the option to hang around for 10days and just get fast tracked to the wall...

The Deities who agreed to the Pact Primeval failed to read the fine print and really didn't want to deal with the issues. The dangers of outsourcing.

I remembe seeing something off FR wiki (so it might be total BS but I will post it so feel free to correct it)

Adon (Kelemvor and Mystra's mutual friend, as well the patriarch of Mystra's new church) was driven mad by Cyric's trickery, losing his faith in Mystra, and had died a faithless soul. Mystra came to Kelemvor and asked for Adon's soul, which Kelemvor steadfastly refused since Adon was now one of the Faithless, or perhaps even the False. This, along with Kelemvor's loss of passion, eventually caused the breaking up of their relationship.

That's only part of it. I've read the novel that bit is out of. Because of Cyric's direct interference that caused Adon to fall and die Faithless, Mystra was allowed to directly intervene to try and restore his faith after death, so he eventually ended up in Mystra's realm, not the wall. So apparently Kelemvor takes extenuating circumstances into consideration.

Now the question becomes what if the SotF worships a pantheon or additional gods? If they still have the dead one as their patron, is there absolutely nothing else that matters?