What are the chances that the market dips drastically when I need to liquidate during retirement age? (20-30 years down the road)

My advice would be to hedge your bets if a big market hit is too painful to handle. You can look at bonds/options if you want to reduce equity risk, or DCIs if you're looking to hedge FX risk (if your portfolio is in a different currency). Happy to share more if you're interested.

There will always be a chance that market dips when you need to liquidate your investment. That is where the "100 minus age" rule of thumb for portfolio allocation comes in, i.e. the allocation of equity in your investment portfolio should be about (100 - your current age). As you age, equity allocation will reduce and fixed income portion increase.

One source of retirement income is your CPF. When you have FRS in your RA at age 55, you can freely withdraw your balance in SA and OA. When you are age 65, you can choose to start receiving CPF LIFE monthly payouts.