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You know... That is not a bad idea! I can't find much reference to it, but you might try it and see how it turns out. Preserving other leaves in Poly is somewhat common, so I don't see why this wouldn't work.

The damage is characteristic of coconut rhinoceros beetle, which will infest banana plants. I am not sure if this pest is prevalent in your locale. It could be another large beetle or weevil. In any case the control measures will be the same.
Sanitation is important to eliminate the habitat for larvae development, which is fallen wood and debris, open compost and manure piles.
It is not possible to repair the damage that has been done, but it is possible to prevent further infestation. For ornamental plants, not food plants, a systemic insecticide applied to the soil for root uptake is effective. And/or a contact and barrier insecticide spray drenched on the foliage and into the leaf bases will work for a period of time, after which it needs to be repeated.

Contact a local tree service with a plant health care division or a landscape pest control company. Professional applicators have access to better insecticide products and know the best timing for effective applications.

For do it yourself organic method and material, you can use a neem oil product with Azadirachtin, (not the less potent 70% neem oil without the Azadirachtin). But you will need to spay the entire plant every two weeks. It's preventive and effective for a wide range of pests, only as a repellent.

https://www.gardeningknowhow.com/edible/fruits/banana/problems-affecting-bananas.htm

You would have needed to cut it back for winter so it may be OK. Here are instructions for preparing it for winter. I would wait and see how it does in spring. Then if it doesn't regrow properly, time for a new one.

https://www.gardeningknowhow.com/edible/fruits/banana/growing-cold-hardy-bananas.htm

Unfortunately, your photo did not come through. Without seeing it I can only take a few guesses.

These symptoms can be caused by quite a few things, depending on how the damage and symptoms appear, and exactly where.

The most common reasons are overwatering, underwatering, low humidity, too much light (not likely indoors), not enough light, root rot, overfertilization, Ph imbalance, among many other things can cause banana's to act up.

The MOST common issue with indoor bananas is overwatering. They need the soil to dry down to at least 3 inches between watering, and need a container with PLENTY of drainage to allow all extra water out.

For now, we have several articles that will help you to care for your Banana plant: https://www.gardeningknowhow.com/category/edible/fruits/banana

Banana trees need fertilization with nitrogen only or a balanced fertilizer.
https://www.gardeningknowhow.com/edible/fruits/banana/growing-cold-hardy-bananas.htm
https://aggie-horticulture.tamu.edu/newsletters/hortupdate/hortupdate_archives/2003/apr03/art4apr.html

Once it is broken down by the soil microbes, yes, it will be beneficial to the soil. It can be left, or tilled in with the rest of the soil when you divide your banana plant.

This article will help you to care for the plant: https://www.gardeningknowhow.com/edible/fruits/banana/growing-cold-hardy-bananas.htm