Just to confirm: you can use the new rules with Mistfall, if you have the Heart of the Mists components (specifically: the new Quest Charter and the Time Charter).
Now, there is also a variant in the rules that allows you to use both the new Charters and Time Cards, if you want to use their Event part. However, if you want to drop Time Cards completely, you can simply use the new rules.
Wow!! K awesome time to read up the rules for HOM and forget Mistfall rules !! So looking forward to hammering this for several months!!