AoE weapons in Highsec are likely to backfire because they don’t discriminate. Attacker brings a neutral ALT in a rookie ship, AoE weapon kills same, CONCORD takes down the structure.
Easiest way to deal with abandoned structures is require the owner to take some action to maintain a connection with the Upwell network - could be Charters or a minimal fuel cost to “keep the lights on”. Doesn’t matter as long as it is something an owner needs to do periodically. If the connection to the Upwell network is lost the structure still works but no hull bonuses and no 3rd timer - basically the same as a Blood Raider shipyard. Asset safety is debatable - there are legitimate reasons why a player may be unable to login for an extended period, but removing it would encourage more cleanup.