Unless the PAP activate the army to fight for them against sinkies demonstrating en masse on the street, they cannot stay in power. The PAP is not the organs of govt. Its perfectly expected that the trains will run, the airport will operate, lifts will work, etc. after the PAP has been kicked out.
Assuming that the local Singaporeans are brave, daring and courageous to take steps to gather and proceed to an en masse demonstration.
In that scenario, it is very likely the Minister of Law and Minister of Home Affairs will activate and mobilized the relevant units of the Singapore Police Force, possibly including the SPF Gurkha Unit, to contain the unlawful gathering.
After the containment and probably arrests, whether or not the then PAP Ministers and government chose to remain and govern, it is very likely that the system will continue to function.
Therefore, if the stock market and real estate market were to decline significantly, those individuals with the financial resources and guts, will seize the opportunity to buy low.