I think the boots will show up in your collections, but you might not be able to reacquire it--certainly not at max light level.

Regarding what to safely delete, I use destiny item manager. In the search pane you can type is:reacquirable source:eververse.

Just a side note on this feature that's not really relevant to your question, but I thought I'd bring it up.

W/r/t weapons at least, DIM does not seem to take into account all characteristics of an item when classifying it as "reacquirable".

For instance, when D2 deprecated damage type mods and collapsed a bunch of available weapons down to a single damage type, I purposefully kept a few weapons I liked with those mods installed for the purpose of being able to infuse later and have a current max light version of a weapon with a damage type currently unavailable in the game.

So I have Uriel's Gift in all 3 damage types, as well as a few fusion rifles and rocket launchers as well. It probably wasn't worth it, but what the heck, I wanted to.

Filtering my collection in DIM by is:reacquirable considers all those weapons reacquirable-- but the ones I pulled from collections would not actually be the same as the ones I have because of the installed mods.

I think both DIM and the Collections tab in the game properly account for the difference between vendor rolls and random rolls than can be reacquired, but I don't think DIM respects all the possibilities that might exist, at least when considering deprecated mods.

Sorry, I know this is a rather annoying little thread

I was just deleting a set of boots from within my full Vault. I had sorted by 'Newest'. The boots I was hovered over sharded, but the tile of the item directly below the boots flashed as well and I believe sharded too. I'm fairly certain I went from 500/500 to 498/500. I don't know which item it was below the boots, so I was just curious if any of the 3rd Party Item Managers ever were able to get set up to show Dismantled items in a list.
I see Destiny Sets has some sort of Google Drive Backup you can pre-set up, but I don't use 3rd Party Item Managers and didn't have it pre-set up prior to the incident.

Separate sub question; I still have seen no further clarification regarding which items are FOR SURE ok to delete before September.
Would Special Event Armor sets be considered "Eververse-y?" enough that we know we can shard them and they will have an Ornament in September? Festival of The Lost armor, The Dawning Armor Set(s), The Revelry set(s), etc.
Do we know that current season, Season of Opulence, Armor Set(s) are going to get Ornaments like all the past ones?

I think the boots will show up in your collections, but you might not be able to reacquire it--certainly not at max light level.

Regarding what to safely delete, I use destiny item manager. In the search pane you can type is:reacquirable source:eververse.

I was just deleting a set of boots from within my full Vault. I had sorted by 'Newest'. The boots I was hovered over sharded, but the tile of the item directly below the boots flashed as well and I believe sharded too. I'm fairly certain I went from 500/500 to 498/500. I don't know which item it was below the boots, so I was just curious if any of the 3rd Party Item Managers ever were able to get set up to show Dismantled items in a list.
I see Destiny Sets has some sort of Google Drive Backup you can pre-set up, but I don't use 3rd Party Item Managers and didn't have it pre-set up prior to the incident.

Separate sub question; I still have seen no further clarification regarding which items are FOR SURE ok to delete before September.
Would Special Event Armor sets be considered "Eververse-y?" enough that we know we can shard them and they will have an Ornament in September? Festival of The Lost armor, The Dawning Armor Set(s), The Revelry set(s), etc.
Do we know that current season, Season of Opulence, Armor Set(s) are going to get Ornaments like all the past ones?