As AzCal says, carburettors are sustainable indefinitely, whereas ECUs (for any function, not just fuel injection) are much less so. Repairs are sometimes possible, but require very specialist skills and test equipment.
Generic ECUs (such as the Megasquirt) can, in theory, replace a failed OEM unit. However, they need setting up to suit your particular engine, and to do that properly requires some hours on a dyno. If you are lucky, someone will already have done that for your model of bike, and might be willing to share the setup files.
I've been riding - and working on - bikes for 51 years and driving cars for 49 years, and in all that time I've only ever had one ECU fail. It was the boost control ECU on an old Saab Turbo. That is literally the only failure in half a century's worth of bikes and cars. Perhaps I've been lucky, but ECUs are, in general, extremely reliable and durable.
EFI is better in every way in terms of engine performance and behaviour, allowing for much more accurate and sophisticated control of the fuel/air mixture. Therefore I would never normally replace it with a carburettor. If, however, I did suffer an ECU failure and I couldn't get a replacement (new or used), then I would fit a carb. Not before.