fgssand -
It's not a bad question, but, as has been commented on ad nauseum, it's been hashed around over and over again.
What I find interesting is that, with all of the threads and discussions, they rarely get to the fundamental bottom line - which would be the answer to your question.
What defense the Patriots use is determined by what Belichick thinks, with all of his years of experience and astute analysis, is the most effective defense for the particular opposing team and game situation. Period. Period. Period.
So, to determine what Belichick thinks is the most effective defense for a particular opposing team and game situation, you simply have to observe what he uses.
It turns out, with observation, that the preponderance of the time, he feels that the 3-4 is the most effective.
So the answer to your query is that it is most very likely that he will continue to use the 3-4 this year for the majority of the plays - because he apparently feels it is the most effective.
Any observation of how Belichick organizes a team will quickly convince you that he coaches players to be effective in the schemes that he feels are the most effective. He doesn't tailor schemes to fit the players - he tailors players to fit the scheme. It is also very obvious and has been commented on many times in many threads that he drafts for coachable talent and flexible skills so that he has the kind of players that can be tailored to fit whatever schemes he wants to implement.
To phrase it a different way, no matter what particular players 'happen' to be on the roster, that will NOT determine what defensive scheme he uses.
To go along with that perspective, if you are really interested in how Belichick crafts and uses various defensive schemes, you have to observe that, while the 3-4 is used the majority of the downs, it is not at all uncommon to see a 4-3 and, at times, even such schemes as a 2-5 or even one where there are no down linemen. Also, I haven't seen it commented on (altho I may have just missed it), that if you observe the downs where there are 3 down linemen, there is not just one vanilla 3 DL set - you will see the 3 DL in various alignments versus the OL. One example - the NT is not always over the center but may be shifted over so that you end up with a 'strong' side and a 'weak' side of the DL.
As to whether there are 'enough' 3-4 players in the draft to go around - I wouldn't worry about it. Somehow or another Belichick and Pioli seem to be pretty good at finding players that other teams overlook that are really solid, smart, flexible starting players. And if you have watched the drafts, even when the Pats pick low in the round, there always seem to be solid players that drop to them for whatever reason the other teams where drafting as they did. They will find solid players that Belichick can tailor to the schemes he feels are most effective.