I'm thinking about my next trip to KIX on 4/14, booked on UA

BOS-ORD UA 533 10:00a-11:46a
ORD-KIX UA 877 12:33p-

If for whatever reason UA 533 is late for 30 min, I'll miss my connection at ORD.

Then NW looks good now

BOS-DTW NW 385 12:01p-2:11p
DTW-KIX NW 69 3:35p

Shall I hope that UA 533 be delayed?

Is it always the case that if you got kicked to another carrier your booking class (W or K or whatever) becomes Y automatically and you receive double dipping in FF miles from both airlines?