as far as i know, the only way to place a satchel charge which remains active (i.e. can be detonated) is by using a phantom loon, setpos'ing him into place and using
loon_name fire ["put","pipebomb"]
lay the charge. then remove the loon to about 200 metres away, set to stealth and so on to hide him, then activate with a trigger using
loon_name action ["touchoff"]
as for detecting whether it's still active, not sure. anyone?