Yes, you are correct. If the center bolt in the camshaft was loose, then the sprocket will not spin the cam. If that's the case, there's a nearly 100% chance you've had piston-to-valve contact if the engine was running when it came loose, or if anyone tried to start the engine.

Before spending any time/money replacing the timing chains and guides, I would determine the condition of the intake valves in that bank. Then you have to make a judgment call on whether or not you want to fix it. If you just want to do it for the challenge and learning experience without regard to the overall value of the car relative to the cost of the repair, then go for it. Especially if you got the car really cheap and just want to experiment on it.

If it were me and I decided to go ahead with the repair, I would not yank the engine. That is a HUGE FREAKING JOB and there's no guarantee that the newer engine is any better than the one you already have. I would jump on eBay and find myself a new cylinder head. I haven't looked, but I'd be willing to bet it would less expensive than that replacement engine, and a hell of a lot less work to swap out. I'd find a complete head with valves and cams and call it a day. As long as the pistons don't have huge gouges, or god forbid, any holes in them, they'll be okay to leave in service if they're a little beaten up.

Or, if a complete head does cost more, I'd buy that other engine but just swap the parts I needed and not the entire thing.

Since you can't do a compression test without fixing the timing problems, your path of least resistance might be to pull that head and see what you're dealing with. Then, based on the condition of the inside of the head, decide how you want to proceed.

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2002 X5 4.6is - Imola Red/Black (Sold)
2001 740i M Sport - Anthrazit Metallic/Black (Sold)
1998 M3/4/5 - Technoviolet/Dove (Sold)
2003 Z4 3.0i Sport - Sterlinggrau Metallic/Black (Sold)
2009 Mini JCW (The Wife's)
2015 i3 REx - Arravani Gray/Tera World (Daily Driver)