I think you'd have to get an expert's opinion before you could make either of those statements.

Modern radar is sophisticated and might be able to tell the difference between one plane or two located very close together. You'd need an expert, like an air traffic controller, to provide an educated guess here.

If they landed on the water, it's possible the plane would hold together, but a crash into the water would create floating debris. In either case, those US submarine hunting aircraft should be able to find the plane or the debris.

What's the most perplexing aspect of this whole thing is the fact that it appears that the plane's transponders were intentionally turned off, and that leads to all kinds of speculation as to why someone on board would do that. If the pilots were incapacitated, then whoever took over the plane must have had very good knowledge of this kind of aircraft. If the pilots turned the transponders off, what could their motive have been?