What if there is no rebirth but karma is not eradicated by meditation and the path?

Well if there is no rebirth, then it is good news for people who want to stop dukkha: it is only death, the problem is solved without requiring any effort, because humans, devas animals die, whether they like and want it or not.

THe problem is that death of a puthujjana or devas or animals is not the way to stop dukkha, so those people have to do something else than dying, in order to stop dukkha.

What the matter for a Buddhist is to eliminate Dukkha here and now. Not after death. So whether there is rebirth or not is secondary.

There is no 'rebirth' (aka 'reincarnation') but kamma (the idea of 'agent' doing & reaping) is eradicated by the path. This means if the path is not realised, 'the agent' experiences the results of their actions even if there is no rebirth (reincarnation).

However, 'an agent' experiencing the results of their actions is what 'rebirth' really means. 'Rebirth' in reality is the re-arising of the idea of 'the agent' or 'self'.

'Rebirth' does not mean 'reincarnation' into another life. 'Rebirth' means the idea, obsession and neurosis of 'self' keeps getting born; as follows:

There is the case where an uninstructed, run-of-the-mill person — who has no regard for noble ones, is not well-versed or disciplined in their Dhamma; who has no regard for men of integrity, is not well-versed or disciplined in their Dhamma — assumes form to be the self. That assumption is a fabrication. Now what is the cause, what is the origination, what is the birth, what is the coming-into-existence of that fabrication? To an uninstructed, run-of-the-mill person, touched by that which is felt born of contact with ignorance, craving arises. That fabrication is born of that.

SN 22.81

In the teachings in the Pali suttas, 'rebirth' always includes the delusion of 'an agent' or 'a being', as follows:

I saw — by means of the divine eye, purified & surpassing the human — beings passing away & re-appearing, and I discerned how they are inferior & superior, beautiful & ugly, fortunate & unfortunate in accordance with their kamma: 'These beings — who were endowed with bad conduct of body, speech & mind, who reviled noble ones, held wrong views and undertook actions under the influence of wrong views — with the break-up of the body, after death, have re-appeared in the plane of deprivation, the bad destination, the lower realms, in hell. But these beings — who were endowed with good conduct of body, speech, & mind, who did not revile noble ones, who held right views and undertook actions under the influence of right views — with the break-up of the body, after death, have re-appeared in the good destinations, in the heavenly world.' Thus — by means of the divine eye, purified & surpassing the human — I saw beings passing away & re-appearing, and I discerned how they are inferior & superior, beautiful & ugly, fortunate & unfortunate in accordance with their kamma.

MN 4

As long as the mind continues to construct the idea of 'self', 'agent', 'person' or 'being', rebirth will continue. This is samsara. Samsara is circling around in self-views, as follows:

"Just as a dog, tied by a leash to a post or stake, keeps running around and circling around that very post or stake; in the same way, an uninstructed, run-of-the-mill person — who has no regard for noble ones, is not well-versed or disciplined in their Dhamma; who has no regard for people of integrity, is not well-versed or disciplined in their Dhamma — assumes form to be the self, or the self as possessing form, or form as in the self, or the self as in form.

"He assumes feeling to be the self...

"He assumes perception to be the self...

"He assumes (mental) fabrications to be the self...

"He assumes consciousness to be the self, or the self as possessing consciousness, or consciousness as in the self, or the self as in consciousness.

"He keeps running around and circling around that very form... that very feeling... that very perception... those very fabrications... that very consciousness. He is not set loose from form, not set loose from feeling... from perception... from fabrications... not set loose from consciousness. He is not set loose from birth, aging, & death; from sorrows, lamentations, pains, distresses, & despairs. He is not set loose, I tell you, from suffering & stress.

SN 22.99

"A being" is merely a view or idea, as explained below:

Why now do you assume 'a being'? Mara, have you grasped a view? This is a heap of sheer constructions: Here no being is found.

Just as, with an assemblage of parts, The word 'chariot' is used, So, when the aggregates are present, There's the convention 'a being.'

It's only suffering that comes to be, Suffering that stands and falls away. Nothing but suffering comes to be, Nothing but suffering ceases.

SN 5.10