Yes, Julius knew his time would soon be up, as soon as the Saint appeared.
It's abigious what happened next - presumably the military and/or anti-royals so on would take over the country. I suspect it would have created a civil war of some sort. It's also possible they would have launched another attack on the Demon realm, either to deflect attention or due to some aggrivation from the demons themselves.
Of course, the latter could have used the instability to launch a revenge attack, although I suspect there would hardly anything left with which to do so.
Either way, it would spell the end of the Rosweil empire - and no doubt Alicia too (which would tally with her codex entry, although of course she could be dead long before Julius dies), and as stated in-game, the Demon Realm was reverting back to a previous time, so no doubt both worlds would be politically and socially unstable for a very long time.
As for Wilfried, he obviously now has the power to travel through time, so there isn't any reason why he couldn't stop himself. However, I don't think that would be his aim (especially as he wrote the forbidden book) - like Ria's obession with Wilfried, to the debrement of everyone else, all he cares about is meeting her again.
Whether Ria would accept him now, is unknown - as is whether they would actually meet, especially as both are now time travelling.
Hopefully, Ria going back would manage to stop Wilfried and the mess he creates - the witches being the main beneficiaries if she does.
