After my deconversion, I went through a brief period of looking at alternatives to fundamentalist Christianity, but it was only on the order of weeks. I left the faith because of the fundamental epistemological problem. The faith is based on unsupported (and unsupportable) assertions and so is untethered to facts and evidence. This means it's horrible at explaining or predicting or meaningfully guiding lived experience.

And lo and behold, virtually all religions have the same problem. Some of them take themselves less seriously, and allow you to compartmentalize enough to still deal in reality in everyday life. But even those just represent, to me anyway, a dilution of straight-up honesty and integrity in dealing with life as it actually is.

That seems very important.. Religion is obviously as social as it is aspirational. If both are abruptly removed, many would be lost… They can look for ‘us,’ a diversified group, we’ve lots ..to little in common - and spread around the globe!

Some have organized Atheist groups to fill the social void of church and religion, with civic projects and religion-free celebrations & and events. I’d belonged to one, and miss it, but the effort necessary to keep it going waned as our members found religion-free adventures and projects elsewhere and on their own...

It does seem important to have in place a Halfway house ..for those seeking support as they move away from a lifetime of religion… I hope ‘Here’ helps

I feel the type of former believer you are talking about is of the kind who will in time graduate toward Buddhism or another non deist religious ideology or alternately in to some form of naturalist mysticism.
Personally I am of the opinion that rejection of religion or theism or both also will inevitably lead to a rejection of the supernatural and the metaphysical too, it certainly did for me.