It is impossible to predict what will be possible with the technology of the future and this makes it difficult to define limits below where it will not be possible to preserve sperm. However if the laboratory staff feel that the prospects of sperm survival are negligible in the current state of medicine, then it is not advisable to proceed with storage. Each case is judged on its own merits and there may be variations.
There is a small but theoretical risk that samples may be lost during the freezing and thawing process or due to equipment failure with the freezers. The samples are stored in special containers within liquid nitrogen. These containers have alarms in case of failure and so the risk of loss or damage to a sample is very small, nonetheless the possibility does exist.