I am so sorry you did not get better news from your test... :( I know we all here can relate to getting test results that were hard to deal with.
So you doc wants you yo change your ileostomy into a colostomy? I am wondering why--that another big surgery to face...does the doc want to preserve as much colon as possible?
I had my colon, rectum and anus removed...you mentioned that they talked about removing the anus...if it is diseased (mine was with crohn's too), they might want to take it our b/c it can be a cancer risk in the future...and if you have an ostomy, you wont be using it anyway. They do just sew you shut. Also, sometimes people who have the rectum/anus intact have to deal with mucus drainage, but if it is sewn shut you won't have any, obviously.
One good thing with a colostomy is that you can "irrigate" it--basically, you can train it to empty once every day or so, so you don't have to wear a bag all the time like you do with an ileostomy--you wear a stoma cap most of the time.
You seem like a strong person and I am sure that even though this is probably the most difficult thing you have ever gone through, you will get through it and be great.