Unless specified otherwise, the abilities of creature cards and other permanents function only from the battlefield.
If Locust Miser leaves play, its effect ends.
February 9, 2018 4:31 p.m.
Once the creature leaves the battlefield, the effect will end.
Rule 604.2: Static abilities create continuous effects, some of which are prevention effects or replacement effects. These effects are active as long as the permanent with the ability remains on the battlefield and has the ability, or as long as the object with the ability remains in the appropriate zone, as described in rule 112.6.