If a w/t has been already used in a previous pay period, it would not be possible to delete it. You can delimit it from a date which is after its last use in pay results.
Quite often consultants use standard or model w/t's for actual production, after some customizing change like a proc cl or *** cl to suit business requirements. This no doubt reduces customizing effort. But it has its down-side as observed in many client sites. During support packs or in OSS notes, a model w/t or standard w/t gets modified. This will impact such customer installations where it would be required to bring back the old customization or reload the saved T512W table.
Note that before applying support pack, Table T512W is saved/restored using RPU12W0S in/from table T512B.
Moral of the story is: DO NOT USE STANDARD OR MODEL W/T'S, but use them to copy/create customer w/t's. This applies even to some of the /xxx w/t's.