I would assume it will take some time for the disease modifying activity of Imetelstat to actually show effect on spleen size. If the bone marrow heals, there is no need for blood production in the spleen and it will go back to its normal function and form.
Absolutely it is possible...
1) And if blade et al are right in their interpretation of the somewhat strange language structure in the abstract then it has already happened to 8-ish patients.
2) OTOH if the language is as per the alternate interpretation then it is still possible if you wait longer. My point was only that it isn't by any means assured.