Are we sure this news is legit and set in stone?
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No. At the end of the day until there's official confirmation there's no way to be sure. The current evidence is a well known and accurate leaker saying this is the case, and the lack of any real response from NRS denying the claims. I think the first part means a lot more than the second part, but at the same time it wouldn't be the first time someone was wrong. They could stick around, but the smart money is that the leaker is right given their history.
That said, they could also be right right now, and end up wrong. As with most leaks they aren't privy to everything, so if there's some higher level discussion that filtered down as "yeah we're probably done here, hold everything" but that turned around, they may not be in the loop.
With all that said, from a zoomed out perspective, WB is not a great corporate custodian. As others have pointed out, suicide squad was a disaster, and it's hardly the only one under WB. Perhaps more damning, is what KIND of disaster it was. It reeks of marketing and focus groups having the reigns of development. Hot media property + known studio + gambling mechanics + microtransactions? Nothing could go wrong!
Obviously, it did, and it does make me wonder at the hell NRS must be dealing with on their side. I would not be shocked at all that "gameplay" is the absolute last priority for WB and it's a fight to even get what we have. WB reeks of the kind of company that trend chases and has no idea how to properly develop its IP's, and their track record certainly reinforces that.
With that in mind "fuck it we'll take our ball and go home....and write it off on our taxes" is a very strong possibility. I suspect if suicide squad had done remotely well we would get a new shaolin monks in the same (miserable) vein, and I wouldn't be shocked if the next MK title is in a non fighting game vein.
From the pov of the corporate overlords MK is probably a tricky IP. You can't just slap all the common tropes on it because at the end of the day its main selling point is "horrifically violently kill your opponent", but rather than lean into that chasing something like SAW's success, they feel like they're doing almost everything they can to have their cake and eat it to. VS match, go ahead and kill the fuck out of everyone. Story mode, here's a few gory scenes but you'll never actually do a fatality yourself.
It'd be nice if they sold off the IP to someone who gives a damn, but I doubt that's going to happen as history show's there's a lot more shit custodians willing to cash in on brand recognition that passionate people who want to make something as complex as a fighting game (and the only popular block button fighter at that).