Commented by: @pavel-zotov

It's interesting that if some other object does exist in DB and it depends on view V_TEST (which is to be deleted) then, of course, view V_TEST can not be dropped, no crash occurs, but message about the reason why drop denied looks strange: "table V_TEST is not defined".

Example (we add two objects that depends on V_TEST: another view (v_test2) and procedure, then we attempt to drop V_TEST):

===
set autoddl off;
commit;
recreate table test(id int);
create view v_test as select * from test;

create view v_test2 as select * from v_test;

set term ^;
create procedure sp_test as
declare c1 cursor for(select id from v_test);
--declare c1 cursor for(select 1 as id from rdb$database);
begin
open c1;
while (1=1) do
begin
fetch c1;
end
close c1;
end
^
set term ;^

alter view v_test as select 1 id from rdb$database;

set count on;
set list on;

-- Let us check that object V_TEST:
-- 1) does exist
-- 2) is of type VIEW
-- 3) has source that we just assigned: "select 1 id from rdb$database"

select * from rdb$relations where rdb$relation_name=upper('v_test');

RDB$VIEW_BLR 6:1ed
BLOB display set to subtype 1. This BLOB: subtype = 2
RDB$VIEW_SOURCE 6:1ee
select 1 id from rdb$database
RDB$DESCRIPTION <null>
RDB$RELATION_ID <null>
RDB$SYSTEM_FLAG 0
RDB$DBKEY_LENGTH <null>
RDB$FORMAT <null>
RDB$FIELD_ID <null>
RDB$RELATION_NAME V_TEST
RDB$SECURITY_CLASS SQL$3
RDB$EXTERNAL_FILE <null>
RDB$RUNTIME <null>
RDB$EXTERNAL_DESCRIPTION <null>
RDB$OWNER_NAME SYSDBA
RDB$DEFAULT_CLASS <null>
RDB$FLAGS 1
RDB$RELATION_TYPE 1

Records affected: 1

--drop view v_test2;
--drop procedure sp_test;

drop view v_test;
commit;
Statement failed, SQLSTATE = 42S02
table V_TEST is not defined <<<<<<<<<<<<<<<< ??? 8-O ??? <<<<<<<<<<<
After line 34 in file qq.sql
Statement failed, SQLSTATE = 42S02
table V_TEST is not defined
After line 35 in file qq.sql