If they do impose a lockdown, will busses still run?

Yes, but rather depends which part of the country you are in, or indeed which country. Buses are still operating in the current lockdown in England, but with restrictions. The buses in London operated (but did not collect fares) during the first lockdown. Now they are only accepting 2/3rds capacity to maintain social distancing and face coverings must be worn. They have to run to get key workers to hospitals, children to school etc.

With reduced services, normally.

Essential services are given special consideration during a lockdown.  Even 'they' know that rule.

I'd say so because they'd be considered an essential service, but they wouldn't run as often. You could go to your council's website and see what changes they're making to public transport. 

For now, most governors want to close down businesses that poses the most risks starting with bars, churches, restaurants, and gyms. If that doesn’t slow down the spread, then it’ll be other businesses like malls, department stores, hospitals, etc. 

It depends on the lockdown, I suppose.  Where I live, the busses still ran during lockdown AND did not charge fare because they didn't want the passengers getting near the driver.  

In a lockdown all essential services are aloud to continue.
And a bus service is classed as an essential one.

--  It depends on the rules imposed by the city authorities or the state authorities.
--  Buses and other transport  are usually allowed to run during lockdowns, but at less capacity and with strict mask and distancing rules.--  Other businesses will operate during lockdowns, but many will do so by internet while other non-essentials will close shop. Some businesses may not survive the lockdown period if they do not adapt.

No you will have to go down in mom's basement and stay there until they call you out, . the rich will go on in life like everything is fine.. do as I say and not as I do... great quote that is

It would help to know in which country 'they' are.   During the early lockdown in the UK, the busses didn't run.   I don't think they are currently running during the 2-week lockdown here either.

I think that bus will run normally every 20-30 minutes ,

Yes, the drivers still want to get paid.  But they don't actually want to pick up passengers.