My status will expire while my I-485 application is pending

Many people ask whether, after filing a change of status or Form I-485 with USCIS, they fall out of status if their current status (visa) expires while the case is pending.

First, when you file a change-of-status application, you receive a receipt notice. Even if your status expires during this period, you (including OPT holders) are still considered to be in valid lawful status.
This means your status remains lawful until a decision is issued. If the case is ultimately denied, however, you immediately become subject to removal and should leave the country as soon as possible.
In other words, whether you remain or must leave is determined on the day the decision comes out.