To me, there are a few variables I would take into consideration before making a decision, or a recommendation for my future clients.
First, are they breeders or pets? If it's a breeding animal, or there is the chance it will be bred, euthanizing is the quickest and surest way to make sure those genes are not passed on. I had a pregnant female stop eating almost at full-term. I took a look in her mouth and her teeth were shot. I wasn't sure I could sustain her and the unborn kits through to delivery, and I didn't want to pass on the genes and have other people have to deal with it, so we euthanized her, and the babies. I was in tears when I took a look inside her at the nearly perfect kits. But in order for me to keep producing healthy animals it had to be done.
Second, what kind of malo are we talking? If it is root elongation, by the time you notice it it is usually very progressed. Can you imagine what having your teeth growing through your bone feels like? Nothing can be done, so i would definitely euthanize immediately.
If it is growth of the occlusal surface, I may consider filing. If the animal bounces back from the procedure with minimal lag time, and the filings are a good distance apart then I don't think that is a bad decision.
Third, what are the persons resources? I myself, don't have the time or money to go through multiple filings (and recoveries) a year. With so many animals I have to think of the "herd health" and not so much the individual. In select cases, the individual will be looked at, but in the case of malo, which is incurable, it's better for me to consider the herd's health.
The thing with animals is that they cannot tell you what kind of pain they are in. You can infer that once they stop eating, they are in immense pain, but how long were they in pain before they couldn't handle a basic self-preserving instinct like eating anymore! I agree with what's been said on here before "Better a day too soon than an hour too late". The special thing about veterinary medicine is that we can relieve animals suffering. Why should make them go through even one day of pain (in a terminal disease) when we have euthanasia at our disposal.