He has now a home, Maria and Dia (kinda) to take care of, he has quite a bit to lose and basically not much to gain other than somewhat strong helper who could very well die if her creators decide so.
Had Kanami not developed any emotional connections to Lastiara, it be a logical(heartless) decision to give up on her, but that isn’t the case.
You’d also have to account for Maria(and Dia ig) and how her death would impact them
She's a jewel/flesh puppet so it wouldn't surprise if they had some remote killswitch for her.
A fair assumption! But how would it work?
Would it just explode her into gory bits?
Well they plan to revive Tiara using her body so that’s out
Then how about removing the personality/mind?
But why put one there when they intend to replace? Is it a core component? Would the body decay without a mind?
Speaking of, how expensive
is a Jewel Cruz?
There’s the flesh, probably from the higher class and the talented
The jewels, being refined magic stones of the highest quality
They’re also using Tiara’s blood which is in limited quantity
Not to mention, the amount time they poured into this project
And the only way that they
would have a remote killswitch would be through the Magic Formulas
Which were crammed and specialized into reviving Tiara so there’s most likely no leeway there
Conclusion:
While the killswitch is an interesting idea, there are too many constraints, expenses or variables to make it a viable failsafe
All in all, your comment was a fun brain teaser, I enjoyed it
Thank you!