Mariamagdalena - yes, one day, I would love to do that sort of thing. Right now isn't the time, but one day 
Keeping, yes, I think that is fine. Do you go on to say what you need to do? ie. do you have to assist him with finding the toys? Would you have to search for the toy until it is found? Do you have to act to keep him safe in crisis? Do you have to act to prevent the crisis, or prevent him or others from injury?
This is my main point, I suppose. (I am sure you have said all this stuff, but for others reading) It is sad that your DS gets frustrated about losing his toys. But so do lots of NT kids. My DD2 is 3.7 and we had to go to a friend's house to borrow keys for the Church building, because she had left her dolly there, and didn't want to go to bed without it.
HOWEVER, the key point to stress, is that for my DD2, while she may have been devastated, and even may have had a tantrum, her reaction would be normal for her age, and would pass relatively inconsequentially.
For a child like your DS, presumably, you would do ANYTHING to find that animal, to prevent the crisis which is so distressing, 'abnormal' for a child his age, and violent that the mere thought of it is something you dread?
It is THAT which is so important to get across on the forms. Because otherwise, you run the risk of the DM thinking 'so he doesn't like losing his toys, what kid does?
You need to spell out every difficulty, every stage. Here is what I put for DD1's medication:
"DD1 has to have her epilepsy medications and liquid Melatonin before bed, and she does not enjoy this, so she will run away, shouting ?HIDE!? when she sees the medication being drawn up. She requires encouragement, and often gentle restraint, to allow the syringe to her mouth. She needs close supervision to ensure that she swallows the medication rather than spitting it out. Her 2nd epilepsy medication is in chewable tablet form. She requires close supervision to ensure that she has chewed and swallowed the tablet, which is very small. If she is not co-operative, we have to dissolve the tablet in 5mls of warm water then draw it up in a syringe."
Now, I could have simply said 'DD1 has to take medication and she doesn't like it'. But the care needs come from the different steps I have to take, her reactions, and my actions to overcome her reactions. The DM can't be expected to know that stuff. So I have to spell it out. Otherwise, s/he may think 'medication - only takes a second'. No, it takes a good 10 minutes on a good day.