Necromunda, and to a certain extent Inquisitor, still have the core 40K sets available, pretty much forever. The only two games that are really going to be hit hard are Epic and BFG, and even Epic has a list of very usable proxy and substitute minis which are close enough without stepping on GW toes.
I'm not keen on the Epic proxies myself CS, but if new players turn up without a grounding in the GW universe first, then they may be more amenable to going down the proxy route.
My take on Warmaster and Epic (the only SG games I play) is that for established players it is not an issue. It will however, mean that fewer and fewer numbers of 'new bloods' are likely to come on board, except in club situations where we can showcase the SG games. Long term (10 years +) it'll reduce and reduce to a tiny but hardcore fanbase.
It has an impact on some established players too.
Take my case. I played Epic second edition for years before getting into EA somewhere around 2008/9. Converting from second edition to EA required additional purchases for my Eldar and Chaos armies, few of which I've actually made, owing to a lack of cash. The end of the line from GW means that I'm no longer going to go down that route, and I'll stick to playing second edition, and Net Epic, rather than EA.
As for Warmaster, I'd had some inclination to get into it for a while, but didn't have anyone nearby who played it, so I kept putting it off. There could be some better proxies for Empire, and Undead (my two fantasy armies) than there are for Epic (I've never looked, so I don't know), but even so, I just find GW's actions to have rather sapped my motivation to even think about branching out, despite the fact that Fantasy battle as a core game becomes less and less interesting to me, owing to its excessively complicated rules.
