"A pity indeed, but there is little to be done about it now."

Even if he spent quite a lot of time in the aftermath feeling useless because he couldn't think of anything.

"So, the memory you gave up- what happens if you try to recall it now? Is there simply nothing?"

He doesn't know that the effects of the tree weren't permanent, he just assumed that the reason Dextera came back was because his Shard was intact.