If the final beat in a gatra is a rest, the seleh is the last note played. It is not uncommon in gamelan repertoire to find entire gatras of rests. Note that the actual length of time it takes to play a gatra varies from less than a second to nearly a minute, depending on the tempo (laya) and the irama.
If the final pulse in a gatra is stillness, the seleh is the last sound emitted. It's not unusual for entire gatras to be comprised entirely of quiet moments in gamelan music repertoire. The actual duration of playing a gatra can vary significantly from less than a second to nearly a minute, influenced by tempo and rhythmic pattern.