Reopening a question nullifies all pending delete votes on that question, and [that seems to always have been the case][Shog] (though I too thought it didn't).

Otherwise, delete votes are (currently at least) permanent, they cannot be retracted, nor do they age away. That may change in the future, as

> Personally, I still think the delete workflow needs some work - bookmarking this for future reference. [Shog9♦ Feb 25 '13 at 18:12][Comm]

But that's not a high-priority issue, so it will take at least [6-8 weeks][Meme] before it is tackled.

[Shog]: https://meta.stackexchange.com/a/113012
[Comm]: https://meta.stackexchange.com/questions/112995/should-we-allow-a-mere-5-reopen-votes-to-nullify-any-number-of-delete-votes/113012#comment498349_113012
[Meme]: https://meta.stackexchange.com/a/19514