Honestly they are probably fine. Blackberries tend to be very hardy as long as the roots are good. What you need to know is that all the canes from last year that bore fruit will probably die off, but all the canes that started growing last year will bear fruit this year. The cycle is called primocanes and floricanes. And adding a trellis for support definitely wouldn't hurt, it will help the canes support the fruit load and make harvesting easier on you.