SwiftKey: Keyboard completely gone after update!
There must be some other issue that caused your SwiftKey app keyboard to be disabled or uninstalled. I just updated mine (deliberately)  to version 7.2.4.22 to test this and the app is working fine. I also restarted the phone and it still works. 

Here are some solutions I can think of:


If you had an another keyboard installed, such as Google Keyboard (usually comes with most Android devices that ship Google apps), and provided you didn't disable the keyboard under Available Keyboard settings, you should be able to boot into safe mode and use the device. The stock keyboard app would kick-in automatically. Search internet for safe booting in your device.
Alternatively, since your device supports OTG host you should be able to use an OTG cable with any standard wired keyboard to enter your password/PIN. For a pattern, use a wired mouse.