Hello, cindylouhoo. Assuming that it gets adequate sunlight, constant moisture (moist, not wet, soil), has no pests and is not located inside near an a/c vent, it may be loosing leaves just because it is deciduos and that is what it normally does in the Fall/Winter. It is difficult to determine if it can survive Z6 Winters if there is no plant label that states its hardiness. Florist azaleas may do well in warmer locales (say zones 8-9) when planted outside but since you have no idea of its hardiness, all you can do is plant it outside, mulch it well 3-4" and see if it survives. Alternatives might be to grow it in a greenhouse if you have one; or grow it in a pot and bring it inside during winter. Check the underside of leaves and top soil for indication of very small pests. My condolences on the passing of your father. Mine passed away just two months ago.

Cindy, I'd like to add my sympathy to your loss too...

As for the azalea, sometimes it's best not to place too much sentimental importance on a plant - can easily lead to disappointment. These have been grown with the focus on bloom display and subjected to a regime of growth hormones, special lighting and temps, fertilizer schedules - and not necessarily with the overall long term health of the plant in mind.

My own house is almost guaranteed for distressing azaleas left indoors, humidity is much too low with my heat pump/electric back up furnace. They do best in most homes when given even and consistent moisture without standing in overly saturated soil (of course remove the florists foil from around the pot) bright but indirect light, a cool room, high humidity....very few of us can provide the right conditions for keeping them inside long term.

As a florists plant it has been greenhouse grown and never has seen the outdoors - it would need to be hardened off gradually after danger of frost much like you would treat an annual plant before installing in the garden. As Luis has said, it may or may not be winter hardy in your zone.
You can try to raise the humidity around it, gradually acclimate to outdoors this Spring, either plant or containerize it to bring back in next Fall.

Thank you all for your responses. I figured it would be difficult to maintain it. I'll try to take care of it until I can harden it off in the spring and then plant it. And thank you for your condolences, too.

Hi Cindy,

My condolences.

A must is to make sure there is a drain hole and adequate drainage. Wet roots are the main killer of azaleas. It may be good to repot in a larger pot with lots of gravel in the bottom of the pot. If the roots were kept too moist, it may have root rot. This is usually a terminal condition.

They usually need a little acidic plant food since they are constantly being watered. Miracid is probably the best, but only use much less than the recommended rate. Use no more than half the recommended rate. They like lots of light, but not a full day of direct sun. They are usually not hardy enough to leave outside during the winter, but putting out during the warmer months is good idea.

Here is a link that might be useful: Care of Greenhouse Azaleas