I guess it isn't so simple [0]

    msg_no_basic    db      'No ROM BASIC', 0Dh, 0Ah, 0
    
    ;=========================================================================
    ; int_18 - execute ROM BASIC
    ; Note:
    ; Prints an error message since we don't have ROM BASIC
    ;-------------------------------------------------------------------------
    int_18:
     mov si,msg_no_basic
     call print
    .1:
     hlt
     jmp .1

[0] https://github.com/skiselev/8088_bios/blob/dfff4fddc8ea73c8a...

Someone could take this and try to make it ROM-able in order to "complete" the BIOS:

https://github.com/microsoft/GW-BASIC