I think that the most hopeful 'spin' on losing Posey is that it does force some changes. So instead of 'let's just do it again', we have a new look from the bench and the thus need/motivation to redefine and grow as a team. I think subtle changes to a championship team is healthy. The 'new' team is now put to the test and given the requisite time to evolve. Repeat is certainly a possiblility, and if we rest on the assumption that the big three will be equally effective as last year, there does need to be either an individual who makes a leap (in overall play or improved consistency) or collective growth that compensates for the loss of Posey (and one could add playoff PJ to what has been lost and must be overcome).
I think that it is exciting to anticipate and then observe who of Rondo, Perk, O'Bryant, Pruitt, Walker, Giddens, TA, Powe or BBD will step it up. Lots of possibilities there! But, in answer to the OP's question -- I do think this is the opening day roster but I also hope that a veteran C or a solid backup SF is added. I like current roster at the 1, 2 and 4.