I can see three or more of the starters on the team in 2019.
Hav and Brown they probably want to resign since they will be young and at this point don't appear that they will be expensive (IOW, not stars worthy of huge contracts) Saffold could easily be retained too.
Whitworth is signed to 2019. They may draft his replacement before then but if he's still playing at a high level - which isn't uncommon for O'linemen to do into their late 30's - why would they get rid of him early?
I think they would want to retain a high degree of consistency if possible since OL's perform better when they do.
But more than anything, I wonder how they would be able to make the OL a priority in the '18 draft when it appears that they will need to replace several positions on D.