Since they apparently changed the perk with 3.2.0 it now gives tokens for hooked survivors while the obsession is alive.
 
As with any other obsession perk that gains, or keeps an effect after a certain condition is kept (e.g. Save the Best for Last). A new Obsession will reactivate the perk to the state before killing the obsession. So you will keep your Tokens as well.
DBD Perks are usually pretty clear about this kind of stuff. 
It states:

>**If the Obsession is alive**, all Survivors get a 2 % stack-able penalty to Repair, Healing, and Sabotage speed for each Token.
>The Killer can only be obsessed with one Survivor at a time.

*as taken from the [DBD Wiki][1]*


Its's the same with "Rancor", which will let you kill the Obsession if the exit gates have been powered and will let you kill the Decisive Strike Survivor even if you already killed an survivor with the perk.

With the old Version of the perk, it actually resets to the point where the penalty for the survivors will be removed again, when the obsession shifts to a living one. Its the same as with the other two perks and depends on it state the obsession is in.

  [1]: https://deadbydaylight.gamepedia.com/Dying_Light