Disclaimer: I'm a liberal.
Now let's assume Obamacare falls apart (even I can see it's not doing too well, from the enrollment numbers to the website to people losing plans to people's plans price rising)
How do you make sure that people with pre-existing conditions can get insurance? If you remove the mandate but leave that clause in, it will raise the price of insurance on all of us.
Personally, I would go with a public option. That way, insurance companies can keep doing whatever they want to do, those who have pre-existing conditions can sign up for the option, and insurance companies would finally have decent competition.
For my Republican friends, please note that leaving it to the free market is not a good answer.