Pretty broad topic that you won't get any detailed answers easily.
First of all it depends what products of TIBCO you talk about (TIBCO = company name not a product).
Most likely Businessworks, EMS (Enterprise Message Services) or ActiveMatrix Bus.
Then it depends to 100% on complexity & performance requirements that you have and the impact on connected systems to go anywhere near a decent answer.
There will be no PDF to just guide you through the way, as this is exactly a consulting skill needed here. 
From my own experience it will be very very much depending on complexity, performance requirements, counter of interfaces, long term vision and very very much how "deep your pockets" and risk taking willingness are to get a viable answer etc etc.
P.s.: I saw customers do migration examinations and implementations by customers in both ways btw. (from PI to TIBCO vice versa) .
With best regards
Sebastian