"봄날이 오면은 뭐하노 그쟈" == 봄날이 오면은 뭐 해, 그렇지? => 봄날이 오면은 (even if spring comes) 뭐 해 (what good is it; it makes no difference), 그렇지? (don't you think?) It is hard for learners to understand as is, with dialect words (뭐하노, 그쟈) and a roundabout expression. 뭐하노 (뭐 하니, 뭐 해) is literally "what can we do with it?", meaning "it's no use; it won't make a difference". It is essentially saying even if spring comes around, it won't change anything. "Spring"(봄) and "spring days"(봄날) are often used symbolically to mean a new hope or a favorable condition. So it may be interpreted as "Yeah, new time of hope might be coming, but it wouldn't matter to us, don't you agree?".

More about 그쟈 and 하노. * 그쟈: dialect term for 그렇지 (그렇지 -> 그지 -> 그지). "그지?" is used fairly widely as a contraction of 그렇지? (isn't it?). * 뭐하노(무엇 하냐?): -노 is a dialect ending form for asking a question like -하냐 or -하니 in standard Korean. Ex: 이자 가노? (이제 가냐?), 인자 우짜노? (이제 어떡하냐?) in dialect speech. But you'll have to master the standard language first :-)