At the time wasn't Maserati actually owned by Ferrari directly anyway - before being spun out to be owned by Fiat directly. Anyway, I think that the fact they are now free of Ferrari is in fact the problem.
I have heard conflicting reports about the 4.2.
At the end of the day, it has FPT (Fiat Power Trains) stamped on the block. What I was told from a reliable source is the 4.2 was in development under Maserati. Obviously, Ferrari came knocking and took Maserati under its wing. Probably had some input, allowed it to be trialed in the 4200 then once proven, had their own version.
There was no point designing 2 different engines for the same application.
Maserati have had variants of that 4.2 in 4.7 guise over many years. Ferrari then allowed their V8T to be in the Guilia, albeit with 2 cylinders lopped off plus in the Levante with all cylinders. Obviously Ferrari feel they have met their obligation coupled with the advance news that FIAT would team up with Renault-Nissan so pulled the plug.
What happens next is anyones guess. With the RN deal appearing to have been scuppered by the French government.
I feel that negotiations with the French are still ongoing behind the scenes and something may still come of it all. Personally, I think its a good fit and would leave Maserati at the top of the brand group and free to put what engine and what power they like into their cars without Ferrari looking over its shoulder.