go down (v)
go under (v)
settle (v)
sink (v)

Definition:
Example: go under, "The raft sank and its occupants drowned.

hide (v)
hide out (v)

Definition: be or go into hiding
Example: Probably his horse would be close to where he was hiding. She is hiding out in a cabin in Montana.

blow over (v)
evanesce (v)
fade (v)
fleet (v)
pass (v)
pass off (v)

Definition: disappear gradually
Example: The pain eventually passed off.

elapse (v)
glide by (v)
go along (v)
go by (v)
lapse (v)
pass (v)
slide by (v)
slip away (v)
slip by (v)

Definition: pass by
Example: three years elapsed.

slither (v)
slide (v)

Definition: to pass or move unobtrusively or smoothly
Example: They slid through the wicket in the big gate.

subside (v)
sink (v)

Definition: descend into or as if into some soft substance or place
Example: He sank into bed. She subsided into the chair.

retrogress (v)
relapse (v)
regress (v)
recidivate (v)
lapse (v)
fall back (v)

Definition: go back to bad behavior
Example: Those who recidivate are often minor criminals.

disappear (v)
go away (v)
vanish (v)

Definition: get lost, as without warning or explanation
Example: He disappeared without a trace.