Tuvix was fully capable of hiding his Katra in someone before he allowed himself to be executed. In fact using his own demise as a distraction/diversion while he took root in someone's psyche might actually explain why he so calmly dug his own damn grave.
Tuvix's Katra could have not only been in any one, but been in a lot of anyones.

(You can pick/tick as many options as you want in the poll.)
Tuvix's Katra could have not only been in any one, but been in a lot of anyones.

(You can pick/tick as many options as you want in the poll.)