All anyone can do is plan for the obvious (there will be times DC needs time off childcare/school, you will be exhausted for the first few weeks), and have some contingency plans for the more probable.
If everyone had to have a plan for every worst case scenario then no-one would ever have a baby. People with long running MH problems might cope well, and someone who has never experienced a day of depression in their lives may have severe PND and be unable to function for a while.
A friend's husband died of cancer when their son was six
. There were days when she sat in the car after dropping him off at school and just sobbed and sobbed, then dried her eyes and went to work and got her job done and earned the money to pay the bills. She coped, others in those circumstances wouldn't have. Not something you can predict or plan for.
There are advantages and disadvantages to being a single parent. I would guess (never been a double parent!), being a double parent with a saintly, caring, responsible father would be great. But in reality many people's relationships have difficult patches when the relationship is as much a burden as a support (and babies often trigger that difficult patch). And being a single parent is way better than being a parent with an abusive partner.
Speaking to a counsellor might be a good idea though, to help you clarify your thoughts and expectations.