In the endoplasmic reticulum were removed from the cell which organelle would not be able to function properly and why

No endoplasmic reticulum (ER) would result in the cell's death.

There are two types of ER, rough and smooth.

Rough ER (RER) is studded with ribosomes and this is the site of protein synthesis. The RER is very important for proteins that are to be secreted - these proteins have a signal peptide (the first 5-10 amino acids) that gets processed inside the ER lumen - a signal peptidase removes the signal peptide and then this goes to the Golgi to be delivered. No RER - no proteins get secreted to the cell wall - so no transporters, etc. Not a happy cell.

The smooth ER functions in lipid biosynthesis and metabolism. It is also the site of steroid hormone production and detoxification. It is also the site of the initial glycosylation of proteins. If this doesn't happen, the protein doesn't function properly.

No ER = bad news for a eukaryotic cell!