I really don't think this is to much to worry about, you have marketable skills and I'm assuming you must have good work ethic to get where you are today.
Lets say there is a dip in the market, you have $600k paying 1.7% in dividends. This gives you $10,200 per year of dividend income, regardless of if the prices fluctuate or not. That only leaves you with $13,800 to come up with per year in income, assuming your expenses are $24k per year. That is $1150 per month, and with roughly 180hrs of working time in a month that means you would have to figure some way to earn $6.38/hr full time. Or if you work part time you need a job that pays $12.76/hr for 20 hours per week.
Are you concerned that you or your wife might not be able to make those numbers happen at a minimum?
Another option might be to take $100k and put it into a rental property that can bring $1k per month of income. These can be found if you spend some time looking, might be a nice diversification, and rents tend to go up over time in areas that are growing. Just a thought.