The exact answer depends on whom you want to believe. Mimansa school has changed over the years. The later authors and commentators of the mimansa school certainly believe in nishkama karma and think devotion to Govinda or dedication of the ritual fruits will lead to moksha. The earlier founders of the school may not have believed it.
Laugakshi Bhaskara's artha sangraha is a commentary of the Jaimini sutras. It ends with the following (see the last two pages, page 293 and 294).
This paragraph describes the two-fold fruit to be obtained from the
practice of dharma i. e. sacrifice and others. If we practise dharma
with reference to some specific fruit, it becomes the cause of winning
for that fruit. But if we perform it [with devotion], not with the idea of getting any
fruit for self, but with the idea of dedicating it to God, it becomes
the cause of..moksa or final release from the cycle of birth and
Apadeva ends his Mimamsa Nyaya Prakasha also similarly that dedication of fruit to Govinda leads to liberation.
It should be noted that both Laugakshi Bhaskara and Apadeva were both followers of Kumarila Bhatta but lived centuries after him. However, the translators believe that this interpretation of mimaska is wrong. They believe that the authors of these texts been influenced by the Bhagavad Gita.
Mimamsa does not believe in nishkama-karman. Further, according to
Mimamsa the highest fruit is heaven and it is obtained by the
performance of certain sacrifices such as Jyotistoma. The idea that
heaven is an impermanent abode and that one comes down from there on
the exhaustion of one’s religious merit is a later growth. It was the
result of the increasing importance which came to be attached to
knowledge as opposed to action. The fruit of knowledge is permanent.
The fruit of action, not excluding the highest viz , heaven, must,
therefore, impermanent. Such was the kind of reasoning, which resulted
in reducing heaven to the posit on of an exalted world, where we go to
enjoy the fruit of our merit and whence we have to return on the
exhaustion thereof. Further, the idea that there is God, higher than
and distinct from , the sacrificial deities such Agni and Indra, to
whom action is to be dedicated and who, being pleased by our
desireless action would grant us liberation, is also unknown to