Am still a beginner who doesn't know much about merit decay but when Ever I want to send merit to someone, I usualy see a warning of merit decay on the merit sending Dash board. check this below the second to the last line, it is written that they have the right to decay unused merit, there is no point hording Smerit. Keeping it does not benefits you, and they deserve to decay unused merit in the future. Meaning its possible. Just that I doubt if people have left their sendible merit to see if actually this warning works.