Help With Snagged Out Daytona!!!

So for a bit of shed fun I bought a shagged out 2006 Daytona 675
So far I have come across a few little things which I would appreciate any of the learned types throwing in their opinions...
Pictured is the rear of the bike with the shock removed, circled in blue is a sensor it has been cable tied up, does anyone know what it's for please?

I have replaced the radiator and fan, flushed the coolant system four times. Afterwards I found a very small ball bearing in the tub that I used to drain into, however I also use it for collecting rubbish/ debris etc. I can't think of any way a small ball bearing could emerge from the coolant system but hopefully someone will be able to confirm this please? It's bothering me!!!!!
I appreciate any constructive input please,
Oh one last one, do you think the Kayaba rear shock is worthy of a rebuild?
KR

Ian