It has been estimated that the original proof of the CFSG spans around 15,000 journal pages written by hundreds of authors over most of the 20th century. The GLS project attempted to simplify this original proof, with a target length around 5000 pages, but this involved a variety of changes to the original proof style, and from what I understand this project has stalled (the last volume was published in 2004 and five more are planned), possibly due to the mounting difficulties of changing the structure of such a large proof.
Has anyone attempted to present an argument for the full CFSG, encoding the high level structure of the proof using journal references as necessary to establish the various subcases? That is, the part of the proof that was happening in the minds of specialists who felt comfortable declaring the problem "solved" after the last journal article had been published (Aschbacher-Smith Quasithin theorem, 1996).
R. Solomon's article above is near to such a project, with a very comprehensive reference list, but it lacks the rigorous presentation of the proof itself, and the division into subcases except in an illustrative sense.
Best Answer
There are two books which together have the purpose of answering this question.
D. Gorenstein, The Classification of Finite Simple Groups. Volume 1: The Noncharacteristic 2 Type Case. Plenum Press, 1983. (Gorenstein died without writing Volume 2.)
M. Aschbacher, R. Lyons, S.D. Smith, R. Solomon, The Classification of Finite Simple Groups: Groups of Charateristic 2 Type. A.M.S. Mathematical Surveys and Monographs 172, 2011.