Hello,
The proper course of action in such a case is to use the collected funds for the same purpose, even if not for that specific soldier. If possible, a letter should be sent to each donor explaining that this is what will be done, and if the donor wishes to have their money returned – that is possible, and of course, ideal. However, if this is not feasible, it is permissible to use the money for the benefit of another soldier in the same situation.
Regarding the donor who contributed a significant amount: from a halachic perspective, a small amount and a large amount are treated the same. However, because it is more difficult to assume that such a donor “waives” his claim, it is appropriate to ask for his permission.
All the best and yashar koach,
Rabbi Yuval Cherlow
Rabbi Cherlow is the Head of the Ethics Department at the Tzohar Rabbinical Organization