Is it possible to raiserror within a For Delete Trigger that rolls back the deletes

Question

There is a claim at the end of this accepted answer that if an error occurs within a "For Delete" trigger, the delete action would be rolled back because it is part of an implicit transaction.

However here is an example showing that the deleted rows remain deleted even though an error is raised:

create table T1 ( i1 int  );
go

create trigger T1_ForDelete on T1
for delete
as
raiserror('Raised 16', 16, 1);
raiserror('Raised 18', 18, 1);
raiserror('Raised #2 16', 16, 255);
raiserror('Raised #2 18', 18, 255);
go

insert into T1 (i1) values (1);

set xact_abort on; -- makes no difference

delete from T1;

Output (order changes):

Msg 50000, Level 16, State 1, Procedure T1_ForDelete, Line 4
Raised 16
Msg 50000, Level 16, State 255, Procedure T1_ForDelete, Line 6
Raised #2 16

(1 row(s) affected)
Msg 50000, Level 18, State 1, Procedure T1_ForDelete, Line 5
Raised 18
Msg 50000, Level 18, State 255, Procedure T1_ForDelete, Line 7
Raised #2 18

Then

select * from T1; -- Returns no records

Is this the expected behavior or is there a way to prevent deletion on an error (e.g. different severity/state)?

I cannot use an "Instead of Delete" because "on delete cascade" is employed. Create Trigger (MSDN), search "For INSTEAD OF"