Hilton leaves decisions about cancelled events (and room blocks associated with them) to properties. But it has provided them with legal information on the 'impossibility' clauses in most Hilton contracts. Declaration of a state of emergency or a government recommendation not to meet in groups of more than 10 people will generally not allow an event host (or participant) to rely on Hilton's Force majeure clause. Generally Hilton defines them within the contract as "impossibility' clauses. They will allow penalty-free cancellation if it is physically impossible or illegal to hold an event. Examples of impossibility: the hotel falls down or the only road to it is on fire. In order for an event to be illegal a government must make an enforceable ban on events. Events in countries, states, counties or cities that have made gatherings illegal (not merely inadvisable) would qualify. Examples would be Italy, and the California cities and counties that have issued "shelter in place" orders.
If you cannot meet either of those standards, then you may try to negotiate re-booking for a later date. Some hotels are allowing that for a fixed future date and will apply deposits to the cancelled event to the new one. Others are offering to apply 50% of the deposits and some offer no credit for a future event.