None deletable gutenberg blocks plugin

block.js

{
	supports: {
		deletable: false,
    ...
	},
...
}

plugin.js

import _differenceBy from 'lodash/differenceBy';

const { subscribe } = wp.data;
const { createBlock, getBlockTypes } = wp.blocks;

export const initialize = () => {
	let currentBlockCount = [];
	let removedBlocks = [];

	const getNonDeletableBlocks = () => {
		const types = getBlockTypes();
		const permanentBlocks = types.filter( ( block ) => {
			if ( ! Object.prototype.hasOwnProperty.call( block, 'supports' ) ) {
				return false;
			}
			if ( ! Object.prototype.hasOwnProperty.call( block.supports, 'deletable' ) ) {
				return false;
			}
			return true;
		} );
		return permanentBlocks.reduce( ( blockNames, currentBlock ) => {
			return [ ...blockNames, currentBlock.name ];
		}, [] );
	};

	subscribe( ( e ) => {
		const { getBlocks } = wp.data.select( 'core/editor' );
		const { insertBlock } = wp.data.dispatch( 'core/editor' );

		const blocks = getBlocks();
		const cantDelete = getNonDeletableBlocks();

		if ( currentBlockCount.length > blocks.length ) {
			removedBlocks = _differenceBy( currentBlockCount, blocks, 'clientId' );
			removedBlocks.forEach( ( block ) => {
				if ( cantDelete.includes( block.name ) ) {
					const oldPosition = currentBlockCount.findIndex( ( b, i ) => b.clientId === block.clientId );

					insertBlock( createBlock( block.name ), oldPosition );
				}
			} );
		}
		currentBlockCount = blocks;
	} );
};