Sure, but it's more complex, than "Can't believe these scientist torture mice for empathy". For now, mice lab animals are our only reliable models.

First they weren't "torturing mice for empathy", they were studying them for examining pain receptors.

Second the study was used to determine if something has empathy or not. Imagine if tomorrow we discovered that large rocks posses sentience, would you not want to determine that rocks have sentience, even if you have been milling them into concrete.

     > Either way, besides killing all the lab mice, we can also just stop breeding them, you know. 

Imagine you are mouse breeder. Your only source of revenue is gone. Are you going to:

A) Release them into general mice populace causing potential short term damage by having too many breedable mice, while their genes are potential long term damage to mice population (mice used to test cancer get cancer really quickly)?

B) Feed them and chemically castrate them and or keep them in isolation (solitary confinement, yay!). Costs money, not sure if departments have that much free dough lying around

C) Kill them painlessly and efficiently?

D) Sell them at a loss as pets, even though they aren't suitable as pets (some of the strains die really really quickly, because they are bred for that).