Yes among the various kinds of liberation viz- SAlokya, SArshti, SAyujya etc only Kaivalya (also known as NIrvAna Mukti) is eternal in nature.
In this context the Tantrik compendium "ShAktAnanda Tarangini" quotes the following verse in the 16th Chapter of the text:
SakAmAnAm sAyujyAdi muktih sAyujyam na parA muktih sharira samvandhAt
AkAmAnAm nirvAnameva muktih parama purushArthatvAt || "Na cha
punarAvartate " --- Iti sruteh ||
The Mukti that desirous persons (sakAma) get are Sayujya etc. SAyujya is
not the eternal or highest form of liberation. Because, [in it]
association with the body is still there. The desireless persons
(NishkAma) get NirvAna Mukti. Which is the highest goal and even in
Sruti it is stated - [He or the liberated being] does not return.
So, the highest form of Mukti, after attaining which one does not return, is not SAyujya and other forms of liberation. It is only the Kaivalya or the NirvAna Mukti.