Don’t do that - be smarter
That shouln’t be a problem - the update is a transaction - so if the pre-validation fails - the transaction is not commited.
Don’t do that
Your incident description is not entirely correct - if your kernel gone missing after your force shutdown - then the sync process has not been cancelled before the transaction - but during the transaction - and that is the problem and a very likely explanation as to why your system froze as well.
As @anon51566685 points out - start your computer using a live ISO - chroot the manjaro system and install the kernel including a full system sync.