Not necessarily; there are other reasonable options.If a player has the option to rebuy and bounties are only for elimination of a player, it means it is unclear if an all in includes a bounty on the line or not. That can definitely matter in determining an action. Most things in poker rules-wise drive towards clarity, so it would seem the only reasonable option is that a bounty is purchased with each rebuy/reentry/reregistration.
If an all-in player still has a re-buy option available, the rules can also state that an all-in player must declare their re-buy intent at the time of their all-in bet -- simply by including their bounty chip with the all-in bet (if choosing to not re-buy), or retaining their bounty chip along with their re-buy chip (if choosing to re-buy if/after losing). The player's declaration is binding.
This simple rule solves the clarity issue for any future action(s) in the current hand.
Although it is true that a player who declines to purchase another bounty chip with their re-buy can subsequently lose and not suffer an additional bounty loss, it is also true that the player is no longer eligible to win any additional bounty chips during the event -- thus increasing the chances of the remaining bounty players to win the remaining bounty chips in play. It simply becomes another strategy decision, and one that is equally available to all players.