Big Pistons Forever, diesel fuel does not detonate in a petrol engine. The engine is probably damaged but not to such a dire extent as to require a full replacement. Most likely, the engine is badly fouled with soot and sludge, hence the debris in the filter (unless this debris is metal shavings, in which case it's a lot more serious). The spark plugs are definitely fouled up. Some scouring of cylinder walls is also possible. There may also be remnants of diesel fuel still circulating in the oil - when you change oil, you cannot drain 100% of it.
However, whatever the situation is, I second A&C's advice to consult a factory representative and definitely not to fly it until fully diagnosed.