When is a Shoel chayav in Onsin?

In this post on kim leh bdrabbah minei Chaim B. writes about the moment of chiyuv by a shoel. He writes as follows:

Once a cow is borrowed, the borrower is liable to return or replace the cow from that moment, which is why even if the borrower dies, his estate is liable. If so, why is a borrower who slaughters a cow on Shabbos exempt from payment because kam lei b’derabbah minei – the obligation for repayment occurrs when he borrowed the animal, not simultaneous with Shabbos? The answer is (see Ktzos 341) that when it comes to klb”m we don’t look at when the potential obligation of repayment occurred, we look at when the actual obligation of repayment is triggered. It is as if the obligation to pay exists on condition (tnai)– the lien is in effect from the moment the obligation is set, but klb”m applies to themoment the condition effecting payment is fulfilled.

I mentioned in my comments that I was troubled by this answer. Here I will elaborate on why. In Meseches Sanhedrin 72a, the gemara discusses the ptur of kim leh bdrabba minei. The gemara is talking specifically about a ba b'machteres. This is someone who breaks into someone else's house as a thief. The gemara's assumption is that such a person is patur from any monetary obligations incurred during the thievery because he is already chayav misah as a rodef (kim leh b'drabba minei).
The gemara seems to conclude that the issue is dependent on the following: Is the obligation to return a borrowed object qualified as mamona gabach, which would mean that the property is really owned by the original owner and it is just a chiyuv to return the object to him (a chiyuv hashava)? Or do we say that for purposes of onsin the item is owned by the borrower. If that's the case there exists a chiyuv tashlumin, a chiyuv of payment, and not a chiyuv hashava. The gemara says that if the shoel has a chiyuv hashava, the chiyuv is not cancelled in the face of kim leh b'drabba mineh because it's not a monetary obligation, it's the mashil's object that is being returned. One is not patur from returning someone else's object with kim leh. However, if there exists a chiyuv tashlumin, it would be canceled by kim leh.
You see from this gemara that when we speak of chiyuvim of a shoel it's either mamona gabach or a chiyuv tashlumin. I don't see anywhere this idea of potential chiyuv and actual chiyuv. There is only one shaas chiyuv. The chiyuv sets in at whatever moment it is kam leh birshusei (at whatever moment the torah says it is considered in the reshus of the shoel).