Hi dot,
Long term complications are a risk of course, but in my view they are almost exclusively a consequence of one or two underlying conditions - abnormal (elevated) blood sugars and abnormal (also usually elevated) insulin levels.
There are many potential cosequences of poorly controlled diabetes, from neurological damage to organ damage, cardiovascular damage etc. etc.
Blood sugars are controllable with insulin, diet and exercise and many type 1's are able to maintain non-diabetic levels using this toolkit. Insulin levels are entirely controllable of course, which is an enormous advantage.
Lots of t1's have the condition for many years with no complications at all, myself included thankfully.
All the best,
fergus