Existence is relative, not absolute.
For me, the import of this discussion is that I assert 'existence' to be on the same level of every other concept which humans denote by a socially acquired languge in specific behavioral contexts.
Thus when
Merdwurdichliebe, for example, asserts that 'a thinker must exist', I suggest this is only valid
now,in a hypothetical scenario in which we might 'observe in our mind's eye' a focal entity we call 'a thinker'.
If on the other hand we have in our current 'mind's eye' a Heideggerian scenario of seamless coping in which 'observer' and 'observed' remain inextricable, or 'unevoked' for much of the time, then we might argue that the 'validity of existence of a thinker' is dependent on those contexts in which 'the thinker' (or 'self' or 'observer') is circumstantially evoked i.e. when seamless coping breaks down and 'considering behavior' kicks in.
BTW. The 'fresco' which wrote the above reply was
evoked by the interactions above. Like 'a tree' its internal state had shifted but its 'conversational identity' via the word 'fresco' remains
functionally the same.