The best I can think of would be to have a feature toggle that can be manually flipped by a developer and route transactions through PayPal when the toggle is flipped. This would solve the ability to collect payments for new customers, but there would have to be some sort of reconciliation/sync when Stripe comes back up to migrate the customers back to Stripe, otherwise you'll have a handful of customers in PayPal indefinitely.
Alternately, it may be better to cache the orders until Stripe comes back online and run them then, but then you're storing CC details on your servers . . .
You could find a way to do a soft failure. In the case of as payment gateway failure, take the order and follow it up manually once the gateway is back up. May not work for every business but an eComm business could just hold the fulfilment until payment is captured. A subscription service could let the subscription run on a short grace period and follow it up.
That could all be done programatically, or give them a call or email.
The best I can think of would be to have a feature toggle that can be manually flipped by a developer and route transactions through PayPal when the toggle is flipped. This would solve the ability to collect payments for new customers, but there would have to be some sort of reconciliation/sync when Stripe comes back up to migrate the customers back to Stripe, otherwise you'll have a handful of customers in PayPal indefinitely.
Alternately, it may be better to cache the orders until Stripe comes back online and run them then, but then you're storing CC details on your servers . . .