I think that it is where and how thick ice is that is more important than how it acts.
Things like ice staying broken will cost huge amounts of code work and resources and to be honest.. what is the point? Icebreakers are nice but not very useful in a subsim.
Simple broken ice parts hanging around when you surface are fine. And the occasional polar bear attack.
I like the idea about having the missile vanish in space. The tactical nukes in addons I guess can't be helped much short of capping the max amount of explosive force.
Hunting a simulated SSBN that can actually launch is going to be fun in that case. I look forward to playing that.
I really suggest giving Lua a view again if it has been some time since youve played with it. Having Lua will greatly reduce the documentation you will need to do since LUA is highly documented and there are totorials. Use the simple parts of lua and mission script writters as far as mission editiors ought to find it easy to make them.