Yes, this is a huge loss for the patriots. The loss of Thomas may cause us to run more 4-3, using Green more. This won't be a major change, but will reduce our defensive options.
However, the replacement as far as reps is Woods, not a free agent.
We now have five linebackers who will be taking almost all the reps: Vrabel, Woods, Bruschi, Mayo and Guyton.
Alexander (still hurt) and Izzo are special teamers and don't get reps at linebacker.
I do agree that we should consider the Practice Squad and free agency in deciding which TWO linebackers to add to the 53 to replace Crable and Thomas on the roster. I expect that Redd will be brought up and a healthy free agent if we can find one.
Under some circumstances, we might look to help from the safeties. Unfortunately, we don't have any backups there: Meriweather and Sanders are all there is.
The bottom line is that we have used all our life lines at QB, RB, LB and S. We are very, very thin for the jets game. Also, we don't have backups at FB and TE (just the two we use regularly).
ONE OPTION
Bring in Seau and have Bruschi, Guyton or Mayo take some reps at OLB.