Yes, Yes, as a theoratical question this is fine, most rad geeks with the Rad Health Handbook and a calculator will come up with a answer that is within reason depending on their assumptions.
However, I see two possible scenarios to a dropped source thru a grate:
1. The Really Poor Manager (RPM) catches wind of it and requires a Plant Problem Report, forms Alara Fast Action Response Team. Has the Rad Engineer recalculate everything plus Fax from the original manufactor. Directs a resurvey over and over then the committee decides to contract a vender in so as to be able to point fingers if anything goes wrong with the recovery. Everyone returns to "Cubicle World" once again their jobs secure.
2. The Field Technician fabricates a duct tape tip on a broom stick, applies the goop from a mouse glue trap, reaches thru the grate . Sticks the source on the tip and places it in the bucket he has prepared with a lead blanket wrap. Sprays the tip with WD-40 to release the glue and hands it to the Radiographer and says "Here you go Pal, don't let it happen again" The Radiographer buys the whole RP crew drinks at the bar that night telling the story over and over how the RPs saved his butt. The RPM catches wind of this and has a Plant Problem Report written for violating 3 Procedures, 2 Shopguides, Chemical Permits and (Gasp!) Management Expectations which results in disciplinary action up to and including Termination of the RPs.