Except for long, long ago when Mythic deleted characters on Andred, Mythic does not purposefully delete characters.
There have been unsubstantiated cases where returning players have reported that characters were missing. It is possible for parts of the database to become corrupted and if the error is not quickly discovered, because the player is gone for years, the lost data could become irretrievable.
Chances are, the toons are on a different server or the toons are on a different account than you recall. The best thing to do is to submit a ticket in game and have a CSR check for your missing characters.
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The art of war is simple enough. Find out where your enemy is.
Get at him as soon as you can. Strike him as hard as you can,
and keep moving. - Ulysses S. Grant
Only the dead have seen the end of war - Plato