The card text reads: "after a space marines unit you control is destroyed, exhaust this support to gain 1 resource" , does destroyed count if a unit has to be sacrificed ( like from losing a command struggle to soul grinder ). I'm just wondering why they used the word destroyed instead of leaves play.

RRG, p. 14: "Sacrificing a card does not destroy the card, and destroying a card does not sacrifice it."

Destroy and sacrifice are two separate things - two different ways for a unit to leave play. The term "leaves play" would include both. By only specifying "destroyed," Secluded Apothecarion is not intended to work whenever an SM unit leaves play. How and why it leaves play matters.