Snippet from the LOA SpaceX filed with the FCC for their system. Here is the link for the PDF if you want to read the whole document:
https://licensing.fcc.gov/myibfs/download.do?attachment_key=1252848
Post-Mission Disposal:
Each satellite in the SpaceX System is designed for a useful lifetime of five to seven years. SpaceX intends to dispose of satellites through atmospheric re-entry at end of life. As suggested by the Commission, SpaceX intends to comply with Section 4.6 and 4.7 of NASA Technical Standard 8719.14A with respect to this re-entry process. In particular, SpaceX
anticipates that its satellites will reenter the Earth’s atmosphere within approximately one year after completion of their mission – much sooner than the international standard of 25 years. After the mission is complete, the spacecraft (regardless of operational altitude) will be moved to a 1,075 km circular orbit in its operational inclination, then gradually lower perigee until the propellant is exhausted, achieving a perigee of at most 300 km. After all propellant is consumed, the spacecraft will be reoriented to maximize the vehicle’s total cross-sectional area, a configuration also stable in the direction of aerodynamic drag. Finally, the spacecraft will begin to passivate itself by de-spinning reaction wheels and drawing batteries down to a safe level and powering down. Over the months, the denser atmosphere will gradually lower the satellite’s perigee until its eventual atmospheric demise.
These microsats don’t carry that much propellant. I’ll believe it when I see it.