FWIW, I posted a means of automatically saving and restoring active/paused timers (employs two automations):
remaining (available for both active and paused timers) to determine how much longer the timer should run after Home Assistant is restarted again.
Normally, it won’t restart a timer whose duration expired while Home Assistant was offline. However, to satisfy requests to modify this behavior, near the end of the thread I offered a modification that allows even expired timers to be restarted for just one second so that they’re allowed to generate a ‘finished’ event (and trigger any associated automation listening for that event).
Personally, I don’t use many timers, and the host machine is protected by a UPS, but I do use this system to ensure active timers are restored.