My generals may be holiday themed, but they are not intended to be temporary generals. Any more than Lord Dracul or QM Clause are temp generals.
You would get these generals the same way we got Lord Dracul and QM Clause last year. Namely, using event resources to buy them in the Market.
Also, other abilities that generals could gain would include: Summon/Calling (bringing in additional units for one battle), ability to become enraged and make a double attack, or use a shield to absorb some damage, etc. Use your imagination.