gametime, between your initial post, the post of collegeparent and some others, I think you are going to identify your answers as well as the biggest challenge for walking on next Fall.
As you describe what happened last Fall, you pitched better than you ever have. That did not get you on the roster.
collegeparent very appropriately points out walk-on players at a DI CA school who don't make it head to a JC, where they "improve" and return showing they can play. It is also true that those scholarship players who didn't get much playing time also need to improve.
In my view, the jump in ability between the freshman and sophomore year in college can be pretty spectacular. In most programs, at any college level, it has to be to continue to earn playing time.
Even when a college program loses 10 players, the coaching staff recruits with the mindset they need to be better the next year.
Many will recruit, or feel they have, over the talent level of the current roster of players. The coaches know they have to get better to keep their job and to do that, they have to recruit better players/pitchers trying to achieve the goal that is set for coaches by the Athletic Director.
In terms of trying to compete as a recruited walk-on next Fall, I don't think you can allow yourself to mentally approach the situation that they lost a lot of pitchers and I can find an opening based on how I performed last Fall. Personally, I don't think you can approach it on the basis they had 18 on schollie and that is the reason.
Next Fall, you will have to perform at a higher level than ever before. There are two reasons: your skills and talent last Fall didn't get you a spot, and everyone returning will have been working an entire year to be bigger, stronger, faster and better. Combine with that the mental approach of that coaching staff which will head into the Fall believing, right or wrong, that they have recruited better players than they lost.
In my view, those will be your challenges. I know of a lefty pitcher at the school collegeparent is posting about who transfered as a sophomore from a DIII. Out of more than 50 walk-ons, he was the only one who earned a roster spot. Two years later he is a weekend starter who has already been drafted in 2007.
Can it be done? Yes, that lefty proves it can.
To do it, you need to be much better than you were last Fall, so that you are at least as good as those returning on a schollie, and those entering with a 25% minimum schollie.
Increasing your competitive ability, and providing "facts" for TRhit to provide his opinion,
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look to be the major challenges you need to consider in your decision.
Good luck to you!