Modern Vespa

After my previous topic (Oil leaking from transmission cover GTS 300 HPE), I took things off and while somewhere I knew I shouldn't start it anyway...... F*ck how stupid.
My Vespa idled very briefly, then silently stalled.
I had already scheduled valve adjustment because I heard somewhat of a ticking noise, but that is now secondary to what needs to be done.
I have just removed the oil seal (which was already uncomfortable) behind the variator, and was afraid to find a mess there. Luckily that wasn't too bad, I am curious to see what else I will find.

I have the following questions, maybe someone can answer them.

- The timing sprocket has come off the keyway on the crankshaft, could it be possible that my valves haven't touched the piston, and that I could time it and then see what happens?

- Or in this case is it always the case that the valves or even more damaged, and you always remove the head?

- If I have to remove the head then is it necessary to disassemble the engine block?

- you can see from the pictures that the retaining ring was already touching my vario, what could be the reason for this?

Tonight I will remove the valve cover, can I see anything there?

That took a lot of work.

Remove the valve cover, cam chain tensioner and cam sprocket and reset the cam timing. The calotte normally rides against the retaining ring on the crankshaft, so that's not going to be an issue.
Once you've reset the cam timing, take the spark plug out and turn the engine by hand, AFTER you've put the seal back on. If you encounter resistance beyond that generated by normal valve spring tension, stop. If you don't, continue. As you turn it, see if the valves are going up and down like they should. If not, stop and remove the head. You likely have a bent valve stem or a broken valve, and possibly piston. As soon as you have any indication that there's something rotten in Denmark, stop and investigate further. You don't want to cause further damage.