create procedure aa
as
begin

	if exists (select * from sys.objects where name='bb')
	begin
		
		drop procedure bb
		go		
		declare @a nvarchar(max)
		set @a='create procedure bb as begin print ''bb''		end'
	end

end

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

create procedure aa
as
begin

        if exists (select * from sys.objects where name='bb')
        begin
                
                drop procedure bb
                go              
                declare @a nvarchar(max)
                set @a='create procedure bb as begin print ''bb''               end'
				exec sp_executesql @a

        end

end

Msg 102, Level 15, State 1, Procedure aa, Line 9
Incorrect syntax near 'bb'.
Msg 156, Level 15, State 1, Line 7
Incorrect syntax near the keyword 'end'.

create procedure aa
as
begin

        if exists (select * from sys.objects where name='bb')
        begin
                
                drop procedure bb
GO

We walk in the dark places no others will enter
We stand on the bridge and no one may pass