No but all neighbors are, except Kosovo (and Bosnia that is on the track for NATO access). A new Serbia-Kosovo war (or Serbia-someone else) is in principle possible and as you say would not imply NATO breakdown. But US and EU have currently a strong grip on the region, the last war sent the message that they were willing to maintain it with force, and I think they have and will continue to have strong interest in no new war developing. And no country in the area should be suicidal enough to go against them. So I think the probability of open war there is very low, unless EU or NATO breakdown has already happened or is happening at the same time.
No but all neighbors are, except Kosovo (and Bosnia that is on the track for NATO access). A new Serbia-Kosovo war (or Serbia-someone else) is in principle possible and as you say would not imply NATO breakdown. But US and EU have currently a strong grip on the region, the last war sent the message that they were willing to maintain it with force, and I think they have and will continue to have strong interest in no new war developing. And no country in the area should be suicidal enough to go against them. So I think the probability of open war there is very low, unless EU or NATO breakdown has already happened or is happening at the same time.
Another scenario would be NATO kicking out Turkey and some Greek/​Turkish war.
Is there any provision that allows members to be kicked out of NATO?