Can man ever stop fighting?
I guess that the answer is no, at least not according to this poem. In the poem, there is nothing that gives us any indication that people are going to stop killing each other (and actually getting better and better at it) any time soon.
As far as out here in the real world (as opposed to in the poem), I think there is some hope that we will no longer have huge wars. We haven't had one since 1945, after all -- not one that really involved lots and lots of people getting killed. But there seems no doubt that we are going to keep killing each other on at least a small scale for the foreseeable future.
This question is a provocative one and a controversial one at that for both thoughtful discussion and a wonderful writing assignment if one has the time to devote to a serious matter as this question asks. Essentially, the poem suggests that humanity may be powerless to stop war, for human beings are indifferent to suffering and ignore those who try to do good. There is a restlessness or madness driving us to war, and we may not be able to stop this drive until we ourselves are in our own “rest eternal” (line 24). Perhaps Hardy asserts that when there is no more man and civilization, then perhaps there will be no more war.