The Gemoro suggests (83a) [if we hold Shimush Nosar Lav Milsa] that the bones of the Korban Pesach could be thrown away (i.e. not burnt).
Now, there will presumably have been blios (absorption of flavour) into the
bones from marrow and even from the flesh of the korban during the roasting.
Do these belios not become Nosar (so that the bones require burning anyway)?
Thanks for an excellent question.
We must establish if Beli'os are, in fact, considered Nosar and if Belios are Nosar must they be burned.
At the end of Masseches Avodah Zarah the Ran (DH Lo Asra Torah) writes that the Torah required Merikah and Shetifah of a Kli Mateches and Shevirah of a Kli Cheres which have absorbed Kodesh because this is the equivalent of Sereifas Nosar. It would seem that according to the Ran Beli'os are considered Nosar and require Sereifah. Since the utensils cannot be burned the Torah provided a different procedure for destroying the Nosar.
If so, why don't the bones of the Pesach require Sereifah? The answer must be that the bones do not absorb. This is how the Mordechai in Pesachim (Siman 1182) understood the problem as he brings our Sugya as a proof that Kelim made out of bone do not require Hag'alah for Pesach as bone does not absorb. The Mordechai does cite other sources that seem to indicate that bone does absorb without offering any solution.
It would seem that according to our Sugya, at least, the answer to your question would be that bone does not absorb.
Kol Tuv Ilan Segal