I received an email from matt moore last year and he explained some of the effects of the trout on fish population. While i don't remember if said 75% of adult rainbows were killed, i know it was a large percentage and definitely over 50%. That being said, i don't believe you will tell a difference. I also remember a study somewhere that said that fisherman only effect a very miniscule percentage of the fish population, so don't worry. However, brook trout and brown trout were found to be basically unaffected by the drought.
Like others have said, the streams were at their carrying capacity before the drought, so now that some have died there is more food per fish and hopefully bigger fish. I really don't think we'll tell a bit of difference though.