So, if you have alfalfa that is "brown", go look at it up and close. Get on your hands and knees.  Look at the crown. See if you can new buds just starting to grow.  While you are at it, grab a crown and see if the root pulls easily out of the soil.  If that plant root pulls easily out of the soil, that plant is done for.  Look at what % plants might be heaved. 

If you are dealing with grass hay fields, you most likely won't see heaving. Still, again, get on your hands and knees.  See if you can see green shoots starting to grow in the crown.   That should give you whether the plants are dead or alive.  Maybe pull up a plant or so. Split it out. Look inside to see if the roots are healthy, or if there is disease inside those roots.

Those kinds of evaluations should help you decide now whether that hay stand will produce, or whether it needs to be replaced.  Even if you see green shoots, but there is disease inside those roots, it is possible it could yet green up, but production might be so low that you should replace it anyway.  Going out now and looking closely should help you make a decision now what game plan you need for this year.