Just curious, What happens to the Sylestie's that you are currently brewing when the Festival Ends?
As well as any unused Catalysts and Brewing Agents you have in the Brewing Area??

Do they Disappear?
Are they transferred back to your Inventory?
Do they stay there until the next festival??
(I'm a little anxious that i will lose them if i can't brew them in time.)

Any and All help is truly appreciated.
Thank you :)

Krin normally gives us a few days after the fest ends to finish up our brewing. Once the extra time is up, all pets being brewed will automatically be turned into eggs and placed in your hatchery.

Sakina already answered your first question, so I'll answer the second one:

If you have any unused leftovers in your brewing area (or any unspent chocolate coins in the shop) when it closes definitely, they will all get converted into old chocolate coins at the start of next year's Fall Festival and they will be sent to you. These old chocolate coins (I think they are called stale chocolate coins or something similar) can't be used for anything except selling them for gold in your inventory.

Thank you so much for answering :D
So the blood vials, calming power, crystals and herbs are unusable for the winter festival?

Winter fest uses snowman building instead of brewing. Each fest has its own different way of creating exclusive kids, so the materials are pretty much incompatible with each other. Even for a few things that have the same art and serve the same function, the names are different and they don't carry over.