Classic tradeoff, and no right answer:
Buying now locks in the price, taxes and fare rules.

Buying later, after JL/MA/RJ join and EI leaves Oneworld, allows travel on those airlines (and prohibits travel on EI). Being able to route on those airlines is a pretty good reason to wait and buy the ticket later (May 2007).

Refund terms vary by ticket type and country of purchase. They are shown in the star file rules referenced by the sticky in the top of this forum. In general:
68N CXLN/ 1. PRIOR TO DEPARTURE
69N REFUND - BEFORE TKT DEADLINE - FULL REFUND
70N . - AFTER TKT DEADLINE
71N . ORIGIN AREA 1 - PENALTY 10 0/0 OF THE
72N . TKTD AMOUNT
73N . ORIGIN AREA 2/3 - NO PENALTY.
74N . - IN THE EVENT OFFICIAL DOCUMENTS/ENTRY
75N . PERMIT/VISA ARE DENIED - FULL REFUND
76N . PROVIDED OFFICIAL DOCUMENTATION FROM THE
77N . APPROVED AUTHORITY IS PRODUCED AND
78N . ATTACHED TO THE REFUND REQUEST.