A torn Achilles is a serious injury, probably more serious than an ACL. Reid did not say that both were out for the season but historically a torn Achilles will end your season. I would not expect DeVito nor DJ back in the lineup this season.
DeVito's loss is easier to handle because of who the Chiefs have him behind him -- Jaye Howard and Vance Walker. Howard in particular is capable of being a sufficient replacement for DeVito. The difference is that DeVito is a 8-yard veteran while Howard is in just his third year and his first with any regular playing time.
Defensive line, linebacker and the whole front seven in general looked to be one of the Chiefs deepest groups. Unfortunately, these two injuries take away two starters, which weakens the group. The Chiefs were counting on their front seven being strong this year so they will need significant production from their backups.