You have already received some good ideas from very experienced practitioners. I have some additional thoughts:
1. First, why did it not go well? What did you learn? Were the conditions that created this "event" understood?
2. Can you get an estimate of the block effect? Do you have other "replicated" runs in the second block that were identical in the first block? If so, you may be able to account for the block effect in the missing data point.
3. Here are some things to try: Use the mean of the data to replace the missing data point and run the analysis, then try your predicted value for that treatment (this assumes you predicted results). Lastly, Remove the highest order effect from the saturated model and regress on the remaining data. Go to the red triangle options for the response >Save Columns>Prediction Formula. This will use the remaining degrees of freedom to predict what the missing value would be. Use that and perform the analysis.
In any case, don't accept one attempt replacement technique. Do multiple replacements and look at the results. If the results of the analysis are similar, you are probably OK, if they are different, then you'll have to think about collecting more data.
"All models are wrong, some are useful" G.E.P. Box