Partnership dissolving, new partnership forming - What separation or severance rules apply?

I would like some help determining when to use the separation from service rule/same desk rule and severance from employment rule. I feel that I am being told that the separation from service/same desk rule no longer apply, but the fact that the two rules continue to be discussed makes me feel that I am missing something. 

If I have a partnership that dissolves (and likewise, terminates its 401(k) plan) and a few partners from that partnership start a new business, hire basically the same staff, and start a new 401(k) plan, what rules apply?

Is the new partnership a predecessor employer for terms of service crediting?

Do the staff members that went from Old partnership to New partnership have a distributable event?

Do the coverage transaction rules of 410(b) apply to the New partnership plan? Do I care about this if Old partnership plan terminated and New partnership started "anew" and both plans were safe harbor? 

Potential wrinkle - or, perhaps, opportunity for planning advice - What if New partnership simply spins out of Old partnership's plan and then Old partnership terminates the "remaining" plan? Any change in answers above? Clearly no distributable event issue since the assets would come to New partnership in the form of a trustee-to-trustee transfer; assuming service crediting would automatically apply; but what of coverage issues?

Is there a reason why one would want to terminate the plan rather than the spin-off solution? Assuming the New partnership would "take on" any disqualification defects of the Old partnership plan in the spin-off, whereas those qualification defects would terminate with the Old partnership plan if it terminated. 

Any help to resolve this question I've been fighting for too long is greatly appreciated! Any issues I'm overlooking?