Hello. I read samui island will be closed completely after 07 April. Airport will be closed after 07 April and bus station is closed to until 30 April. I went bus station and they write no bus until 30 April. 
I have a flight to go back my country on 09 April from bkk. If my flight is cancel , can I come back to samui from Bangkok on 09 April ? I can fly to Surat Thani and use Ferry  to come  Samui after ob 09 April ? Or there is no way to go back samui again after 08 April ? 

So far we have not heard about total closure, just that Bangkok Airways stop, probably due to lack of passengers; Lomprayah catamaran ferries servicing Phangan-Tao-Chumphon also seems to have ceased operation.

 

The car ferries most likely will continue to serve due to transport of goods; however, situation can change fast, April 9th is long time ahead relative during coronavirus pandemi.

 

Are you sure you can find air transfer to Surat Thani by that time?

The local Thai news talks about isolating the island – must be like some provinces and Phuket, no unauthorized entry and exit – says they are signing the papers now.

Confirmed:
The mayor of Koh Samui announced today that the popular island will be effectively sealed off from tomorrow, 7th April until 30th April.
 

To pass in or out travellers must have a letter confirming their health from a public hospital in Thailand. This must have been issued within the last 72 hours.
 

Even then virtually anyone can be recommended for government sanctioned quarantine of 14 days if coming from a risky area or they have been in a risky situation.

56 minutes ago, khunPer said:

Seatran Discovery, not to be confused with the regular car/passenger services offered by Seatran Ferry between Donsak and Nathon. That one is operating, albeit with some reduced sailings.