The plant given away can outlive the friendship that carried it over.

Objects do not keep track of relationships. Something handed over in warmth goes on growing in your window years after the two of you stopped speaking regularly, and it can be oddly hard to look at, because a living thing seems to imply a connection in the present tense. It does not. It is a plant that was given to you when things were different.

You are allowed to keep it without keeping the obligation, and to let it go without that meaning anything either. If the friendship has only drifted rather than ended, a message about the plant is an easy way back in.