Let me start by saying I like Mark Philippoussis both as a player, and off the court as a person. I have met him several times and followed his career with interest. I still remember when he was an up and comer and marveling at his athletic skills for such a big guy. I was also surprised at his lack of coaching and fundamentals, especially in developing a point. His mentality was hit MUCH harder than your opponent and you will win. Needless to say he improved over the years with proper coaching, but he never seemed to have the dedication needed to reach and stay at the top level.
Like all young men, he loved parting and spending times with the ladies, but to be a top pro and have longevity, you must put in more hard work than play. Now that he has been slowed due to injury, and considering his previous attitude towards training(like his surfing kick) and hard work, his prospects for a sustained resurgence is unlikely. However, if he were to dedicate himself (like Agassi did) to total fitness, and a single minded focus of tennis, he might become very dangerous again, especially on faster surfaces.
Like I said, he is a great person, and I wish him nothing but the best. I can only hope that he wants it more than his fans do, otherwise he wont be around much longer.