Plastic tubes are generally considered safe if they are wide enough, but they may get hot and humid with limited airflow, and shouldnt really be left in the cage if there is noticeable chewing.
Cardboard tubes, or woven grass tunnels, are safer for chewing and have better ventilation, but cant really be cleaned so need replacing more often.
Personally I'm not a fan of plastic furniture for piggies myself, but some people are as it can be thoroughly washed and disinfected- mostly a matter of personal choice, but perhaps avoid using them in hot weather.
Sorry you lost your piggy, plastic chewing should be avoided but sometimes happens and a bit of accidental plastic ingestion rarely causes illness because piggies chew things up very small and plastic often passes through the gut without incident, so please don't blame yourself x
