If one of my suppliers' systems goes down, will my whole website stop showing results?

No, not usually, as long as you have more than one supplier connected for that product. A well set up portal asks every connected supplier for prices at the same time and waits only a short while for each one to answer, so a slow or dead connection is simply dropped and the search carries on with the suppliers that did respond. Your customer still sees results and in most cases never notices that one source was missing.

The honest limit is that this only helps if there is a second source for the same product. If all your flights come from one consolidator and that connection is down, flight search will come back empty until they are back online. Hotels are often safer because many portals are connected to several hotel sources, so one going quiet is far less visible to the customer than it would be on flights.

Bookings you have already confirmed are not lost, because they sit in the supplier's own system as well as in your portal. What can be held up is anything that needs to reach the supplier at that moment, such as issuing a ticket, making a cancellation or pulling a fresh voucher. Those requests normally wait in a queue and go through once the connection is restored, although some suppliers will not accept a request that arrives very late and it then has to be settled with their support desk. Nobody can promise you a supplier's uptime, ourselves included, because it is their system and not yours.

Before you worry about it, check how many live sources you actually have for each product you sell, and ask for an alert when a connection fails so your staff hear it from the system rather than from an annoyed customer.